ATA is part of a rich tradition of scientific, tax-related research at the University of Antwerp. Below is a list of completed projects that help make up the historical background of ATA (in reverse chronological order). Unless indicated otherwise, the dissertations are written in English.

Criminal Enforcement of Tax Obligations. A plea for a well considered depenalization

Doctoral research by Jef Van Eyndhoven and supervised by prof. dr. Bruno Peeters. Started in April 2014. Jef Van Eyndhoven has defended his public defense successfully on 2 December 2020.

Belgian tax law is fundamentally ‘criminalized’.  Most tax codes contain a general penalty provision stipulating that every intentional infringement of the tax code constitutes a criminal offense.  This thesis examines whether and to what extent a criminal enforcement of tax obligations is sensible and justified, taking into account the principles and characteristics of criminal law.  The question is being raised whether criminal law, as a ‘last resort’ (‘ultimum remedium’), should be deployed for every tax infringement.  We also try to identify different degrees of tax fraud in order to examine whether certain degrees of fraud may justify a criminal enforcement and others do not.  Where no justification for the use of criminal law can be found, we also examine the suitability of alternative enforcement methods.

Furthermore, it can be noted that the Belgian legislator has provided for a dual enforcement of tax infringements.  Infringements that constitute a criminal tax offense can also be subjected to an administrative penalty.  The result is that tax investigations and criminal investigations, as well as administrative sanctions and criminal sanctions constantly collide.  The usefulness and viability of this dual system of penalties will also be examined.

The research relies significantly on a comparative study in which penalty systems in other countries as well as penalty systems in other Belgian branches of law, especially social law, will be investigated.

Tax treaty power in a federal form of government

Doctoral research by Rik Smet and supervised by prof. dr. Bruno Peeters and prof. dr.  Anne Van de Vijver. Started in July 2015. Rik Smet has defended his public defense on 23 June 2020.

An increasing (desire for more) autonomy for constituent states, regions or other sub-federal entities, including fiscal and tax autonomy, can be noticed in ever more federal states. This raises questions concerning the division of the power to conclude tax treaties in those federal states, as well as questions about the legitimacy of the tax treaties concluded by that state or its sub-federal entities.

Every federal state is unique. Some of them have evolved from a unitary state, others from a confederal model. But all of them are characterized by a division of competences between the different governments. The competence to conclude treaties in general is usually allotted to the central, federal government. And when the sub-federal entities are allotted certain treaty making powers, these are usually subjected to several specific conditions.

Belgium appears to be the federal state which has attributed the largest treaty making competences to its sub-federal entities, based on the in foro interno et in foro externo principle. According to this principle, the sub-federal entities are granted the power to conclude treaties concerning the policy domains for which they are internally competent. This approach and the practical implementation thereof are thoroughly analyzed and compared to the approaches taken by other federal states.

Every government needs financing. Apart from for instance endowments, sub-federal entities are sometimes attributed certain taxing powers. This research investigates the degree in which these internal taxing powers influence and relate to the tax treaty powers of the several entities of the federal state. Also the position of the sub-federal entities in the functioning of the European Union is investigated. In particular is investigated if, how and to what extent the equality between the member states and their fundamental constitutional structure and (internal) division of powers are respected by the Union.

Furthermore the legitimacy of tax treaties will be investigated. A distinction is made between exclusive and mixed treaties. In so far as double taxation conventions should be regarded as mixed treaties, the extent to which sub-federal entities should be involved in negotiating, concluding and ratifying such treaties in order for these to be deemed legitimate, is subject to investigation.

The starting point of this research is a classical analysis of Belgian and international legislation, jurisprudence, advisory practice and doctrine. The comparative research will be functional in nature, whereby only the relevant legislation, jurisprudence and legal doctrine regarding (fiscal) autonomy of the sub-federal entities and moreover the division of treaty-making powers in general and in fiscal affairs in particular, will be investigated.

Two sides of the same coin? An investigation into the joint distribution of income and wealth and its applications to the analysis of poverty, inequality and redistribution

Doctoral research by Sarah Kuypers and supervised by prof. dr. Gerlinde Verbist and prof. dr. Ive Marx. Sarah obtained her PhD on 5 December 2019.

In the academic literature as well as among policymakers financial well-being, inequality and poverty  are generally defined and measured in terms of monthly or yearly income streams. Yet, other financial resources such as savings and assets (i.e. wealth) are also important contributors to people’s living standards. Given that the correlation between income and wealth is far from perfect, any analysis of living standards in terms of just one of these provides partial, and perhaps even contradictory, results. This in turn may result in undesirable policy recommendations. This research therefore analyses the joint distribution of income and wealth and its applications to the analysis of poverty, inequality and redistribution. In particular four main research questions are addressed: 1) How are the distributions of wealth and income related? 2) How to use the available data and methods for the joint analysis of income and wealth? 3) How can information on both economic resources be combined for the measurement of poverty, inequality and redistribution? and 4) How can the results of the latter influence the evaluation and design of specific fiscal and social policies (e.g. wealth taxes)?

The International Crisis in Taxation: A Critical Analysis from a Natural Law Perspective

Doctoral research by Jo Badisco and supervised by Prof. dr. Willem Lemmens, Prof. dr. Bruno Peeters and Prof. dr. Luc Van Liedekerke. Jo Badisco has defended his public defense on 3 July 2019.

Jo Badisco conducted an investigation into the international crisis in taxation. The title of his dissertation is ‘The International Crisis in Taxation: A Critical Analysis from a Natural Law Perspective. He started his research in December 2015. 

This doctoral dissertation investigates from a philosophical point of view the contemporary crisis in international tax law. In the past decades it has become clear how multinational corporations, and persons of considerable wealth, are organizing and planning their taxes to pay as little as possible. This is achieved by using mechanisms such as for example double non-taxation (i.e. the exploitation of double tax treaties between different countries to avoid paying taxes in either country). These findings have caused the legitimacy of the international tax framework to be questioned by specialists as well as by the larger public. The wide-spread tax avoidance has not been without answer and there have been efforts from the Organisation for Economic Co-operation and Development (OECD) with the formulation of an action plan against Base Erosion and Profit Shifting (BEPS), as well as the European Union with the formulation of the Anti-Tax Avoidance Directives (ATAD) to combat the issue. In this dissertation I identify two fundamental notions that run throughout the whole debate: sovereignty of state (a) and the common good (b). The former is important because there has been the question on what level tax legislation should be formulated, states have sovereignty with regard to matters of taxation, but how far should their sovereignty go? The latter is of importance because it gives us an answer to questions such as ‘why is tax avoidance unjust?’ ‘why combat aggressive tax planning?’; i.e. it situates the question in a broader ethical framework.

This dissertation is sub-divided in two distinct parts. The first part is of a fundamental philosophical nature and it defends a specific position in (legal) philosophy: natural law theory. The second part applies this framework of natural law to the contemporary landscape of international tax law by formulating a set of principles that should be adhered to in the international realm of tax law. Based upon these principles I evaluate the contemporary efforts to combat tax avoidance. It is in this second part that the notions of sovereignty of state and the common good are taken up based upon the theory of natural law expounded in the first part.

The first part gives an argument for the position of natural law. I argue that the theory of natural law gives an interesting take on the issue of international tax law. Natural law is more than a theory of law, it is a theory of ethics and political philosophy that also encompasses a legal philosophy. In the first chapter I start off in strictly legal philosophical fashion by trying to formulate a conception of law; i.e. what is law? To do this I start out by going through the definitions formulated by the legal positivist (i.e. law is understood separate from morality and legal philosophy is possible without guidance from other domains of philosophy), by doing so I point out the shortcomings in these definitions and how they naturally lead to the necessity of a full theory of ethics and political philosophy (i.e. the impossibility of treating legal philosophy distinct from other philosophical issues as well as the impossibility of the legal positivist position itself). Further on in the first chapter I argue that the theory of ethics and political philosophy that seems to implicitly underlie the legal positivist is ill-suited for explicating what law is. I argue here that the whole tradition of modern political philosophy (started by Hobbes) harbours shortcomings and is unable to ground what law is. Following this destructive part I start by going through the history of natural law (the foundation by Plato and the full elaboration by Aquinas) whilst arguing how this theory is able to alleviate the issues that came up earlier. In the second chapter I explicate a full (contemporary) theory of natural law as it is formulated by John Finnis. This is done by first explicating his theory of ethics and how it subsequently moves from ethics to political philosophy and also legal philosophy. This concludes the first part of the thesis.

The second part zones in on the issue of international tax law and has as its goals: (a) the formulation of a set of principles that should underlie the international tax law framework, (b) the evaluation of the measures already taken by the OECD (and the EU) and (c) the formulation of a set of limits of what can be dictated by ethics or philosophy. I address the limit to which political philosophy can go and from whereon it has to leave things to political discourse.

The first chapter gives a full overview of the contemporary international tax landscape as well as the remedies undertaken by the OECD (BEPS) and EU (ATAD). The second chapter formulates practical recommendations by means of principles, these principles are deduced by applying the theory expounded in the first part. The move is made from an ethical theory and a legal philosophy to a full political philosophy by investigating the topic of sovereignty of state (i.e. on what level should we try to alleviate the issues with regard to international tax law?), and by questioning what exactly this means ‘finding a solution to the problem of international tax law’ and this in light of these ethical considerations deduced in the first part. The chapter is concluded by giving a critical overview of other positions on the subject. The third chapter starts with an analysis of the BEPS reports of the OECD, I discuss the texts of the OECD; the main topics of interest are the ‘diminished trust’ of people in the tax framework, the principle of ‘taxation according to value creation’ and finally their proposal of a multilateral instrument (which is since June 2017 effectively applied). Following this I give a (positive) evaluation of the OECD’s BEPS report in light of the principles formulated earlier. In the fourth chapter I address two topics that will be of key importance for the future: (a) Is sovereignty of state still workable as concept in the future? (b) What form of punishment is suitable for states who refuse to cooperation in a meaningful manner? 

Data mining for tax fraud detection

Doctoral research by Jellis Vanhoeyveld and supervised by prof. dr. ir. David Martens and prof. dr. Bruno Peeters. Started in January 2015. The public defense was held on 14 February 2019.

With the globalisation of the world's economies and ever-evolving financial structures, fraud has become one of the main dissipaters of government wealth and possibly a major contributor in the slowing down of economies in general. Automated data mining systems that look for fraud patterns in historical data, have been on the rise to tackle this problem. In this multidisciplinary project, Jellis developed, applied and validated new data mining techniques to accurately predict which entities (be it companies or persons) are likely fraudsters, by considering concepts as different data types, privacy, intuitiveness and comprehensibility of the predictions. More specifically, three research objectives were envisioned: (1) the development of data mining methods that can work with massive invoicing data, and the combination thereof with other data types, such as financial and qualitative data; (2) investigation the privacy-invasiveness of the considered data assets and the trade-off with predictive performance; and finally (3) the ability to explain the decisions made by the fraud prediction model.  


De l''abus fiscal' ou quand des actes juridiques des contribuables sont inopposables au fisc pour l'établissement de l'impôt – Essai d'une théorie critique en droit fiscal belge

Doctoral research by Aymeric Nollet supervised by prof. dr. Marc Bourgeois and prof. dr. Bruno Peeters (second supervisor, double doctorate with the University of Liège). Started in 2010 [conducted in French].

Defended on 26 September 2018.

Tax residence of companies as a connecting factor (revisited) from a national and international perspective

Doctoral research by Linda Brosens and supervised by prof.dr. Nicole Plets. Public defense on 15 January 2018.


It is a generally accepted principle of public international law that each State, based on its sovereignty, has the ability to pursue its own tax policy. However, a State is in principle only sovereign within the boundaries of its territory. This implies that a State is only allowed to levy taxes on subjects that have a relevant connection with its territory. The most prominent connecting factor for companies that is used in national and international taxation is the concept of residence.  In order to determine residence, a country can utilize various criteria, such as e.g. place of incorporation or place of management. Although place of (effective) management (or a similar term) is frequently put forward both on a national and an international level, this concept is increasingly difficult to apply. This is due amongst other things to continued globalization, mobility and developments in communication technologies (e.g. videoconferencing facilities). As a result, dual resident issues  can easily arise in an international environment. Moreover, the connection with a particular territory often becomes faint. Therefore, the question arises whether maintaining the residence concept provides an effective way to tax companies. 

Linda performed an in-depth analysis of the corporate residence concept from a national and international perspective and has thoroughly examined whether this concept could either be redefined or replaced by an alternative connecting factor in order to meet these impediments. 

Sales promotion techniques – a search for neutrality for the sales promotor, also taking into account the other key features and principles of the VAT system.

Doctoral research by Nathalie Wittock and supervised by prof. dr. Bruno Peeters. Public defense on 15 December 2017.


Sales promotion techniques (SPTs) are used by companies as part of their marketing efforts to increase sales. Well-known SPTs are for instance price-off deals, bonus offers, premium items with purchase and loyalty programs. Where advertising gives customers a reason to buy, SPTs give a concrete incentive to buy. Although VAT on advertising costs is in principle fully deductible, and despite the clear business purpose of SPTs, the use of SPTs often results in a VAT cost for businesses. Further to the above, the purpose of this dissertation was primarily to investigate to what extent the current VAT consequences of the different use of SPTs are compliant with the principle of neutrality.

Sales promotions are action-focused marketing events whose purpose is to have a direct impact on the behavior of the firm’s consumers.  Sales promotions include for instance free samples, business gifts, coupons, refunds, discounts, money off and cash back vouchers, promotional games, bonus packs, loyalty cards, loyalty rewards and introduce-a-friend schemes. Currently there is no common interpretation on the VAT treatment of sales promotion schemes, having for a consequence that the treatment of sales promotion schemes across the Member States differs widely.In this dissertation, Nathalie identifies the main problems in the VAT treatment of different types of sales promotion schemes, both in a B2B and in a B2C context. The study will attempt to clarify the VAT treatment of sales promotion schemes, also taking into account that in today’s modern market online sales promotion schemes are getting more and more popular among the shopping websites and online retailers.

The principle of neutrality entails inter alia that VAT should in principle not be borne by businesses but by final consumers only. In this respect, the study presents the leading CJEU case-law with respect to the VAT treatment of the use of SPTs. When having to decide on the VAT consequences of the use of SPTs, it appears that in some cases the CJEU closely follows the provisions of the VAT Directive (at the expense of neutrality) whereas in other cases it ignores the legal provisions in order to preserve neutrality. Even when neutrality is currently preserved, it is therefore assessed whether also the other key principles and features of the VAT system, which are reflected in the VAT Directive (such as the fact that VAT is transaction based, the choice for a taxation at destination and the principle that the VAT should not be a primary driver for business decisions wherefore it may in fact not cause some SPTs to be more VAT-friendly than others) are respected, and if not, how they can be.

Based on these findings, a more ideal and clear VAT treatment for the use of SPTs is suggested in this work, not only providing neutrality for businesses using SPTs, but respecting also the other key principles and features of the VAT system.

The tax-legal analysis of regulated bodies for collective investment under Belgian law in a European context

Doctoral research by Evelyne Verstraelen and supervised by prof. dr. Bruno Peeters. Started in October 2009 and successfully defended on 6 September 2017 [conducted in Dutch].

The aim of this PhD is to analyse thoroughly the legal and tax legislation concerning regulated bodies for collective investment under Belgian law. These Belgian bodies will be examined in a European context. The analysis should lead to critical reflections and recommendations which can contribute to a more logical and consistent tax-legal framework for such bodies in Belgium.

The tax-legal analysis will be preceded by the development of a general theory on bodies for collective investment. This section examines these bodies' raison d'être and the national and international (including European) obligations that should be taken into account when determining their status. Moreover, the motives of certain countries to provide special tax-legal regimes for these bodies will be investigated in more detail. The researcher assesses whether these motives are justified and whether the existence of special regulations regarding these bodies can be deemed redundant or necessary. It will then be determined whether the applicable regulations for bodies for collective investment correspond to this general theory.

The legal aspect of the research is subordinate to the tax aspect of the analysis, and the researcher has therefore chosen to focus only on those legal aspects that are relevant to the tax analysis. Where necessary, comparisons will be made with the legal and fiscal legislation for bodies for collective investment in other countries, such as Luxembourg, France, the Netherlands and the United Kingdom. This is a functional comparative study of legislation.

The research also comprises an economic component, including research into the profiles of investors. Certain statistical data will be added to the tax-legal analysis. Where possible, the researcher will examine whether tax regulations or any changes thereof have had an impact on these statistics.

Ne bis in idem principle in Belgian tax law

PhD in law, defended on 8 December 2014 by Anne Van de Vijver under the supervision of prof. dr. Bruno Peeters. 

Double (non-)taxation

Double taxation can generally be defined as the imposition of two comparable taxes on one item (e.g. income, consumption, transaction). Double non-taxation is the opposite situation and occurs when one item benefits from non-taxation, deduction or exemption twice.

 Double taxation and double non-taxation both have harmful effects in terms of the fairness of the tax system, especially when they are the result of aggressive tax planning. In addition, double taxation presents an obstacle to the exchange of goods and services and the movement of capital, technology and persons. In the opposite situation, double non-taxation gives the taxpayer a competitive advantage over other taxpayers who are subject to ordinary taxation. Double non-taxation also has a negative impact on state revenue. In view of the current economic crisis, double non-taxation has gained increasing attention from the European Commission and the OECD.

A number of specific measures have already been taken with the aim of eliminating or reducing double (non-)taxation. However, these measures do not appear to be sufficient. This PhD addresses research questions related to the extent to which general principles of law provide protection against double (non-)taxation.

Presumptions within EU Law and National Tax Sytems

PhD in law, defended on 20 December 2013 by Claudia Sanò under the supervision of prof. dr. Bruno Peeters and prof. dr. Adriano Di Pietro (double doctorate with the University of Bologna).

Claudia Sanò has been awarded with the European Academic Tax Thesis Award 2014.

The thesis deals with the concept of presumptions, and in particular of legal presumptions, in the context of national tax systems (Italy and Belgium) and EU law.

The presumption embodies a concept traditionally considered only from the national point of view, within the framework of the theory of proof. According to a tradition which dates from Roman law, it refers to the inference which is drawn by the law or by the judge from a known fact to an unknown fact. Precisely depending on the source of the inference, presumptions are traditionally distinguished between presumptions of law and presumptions of fact. In the thesis, given that the perspective is the one of the relation between different legal orders, the focus is on legal presumptions. The aim is to give an insight into the national approach to the concept within the national tax systems of Italy and Belgium, and to construe the EU approach to the same concept. This, with a view of comparing them, verifying which conditions are set out at EU level as regards legal presumptions and ultimately testing some of the national tax law presumptions included into the Italian and Belgian legislation against such conditions.

Given that the general definition of  presumption result from the civil law discipline, in the first chapter the concept (main features, function, effects) is examined having regard to the national experience of France, Belgium and Italy, which are assumed as representative of civil law systems, and of the  United Kingdom, which is assumed as representative of a common law system. It is showed how, notwithstanding some negligible divergences, there is a common and shared concept of legal presumption, which is the point of departure for the examination from the fiscal and EU law point of view.

In fact, though the roots of the concept of legal presumption is in the civil law discipline, it shows several peculiarities in the field of taxation, wherein it operates exclusively to the advantage of the tax authorities due to the deficit of knowledge suffered by the latter as regards the relevant fiscal facts realized by the taxpayer. In the second chapter, legal presumptions in the context of the Italian and Belgian tax systems are examined, with a view to construe a national approach to the matter. To this end, at first instance the more relevant Constitutional Court’s decisions concerning national tax presumptions are examined, in order to catch up the parameters used for their evaluation. Afterwards, some of the most interesting tax law presumptions included in the national legislation are examined, with a view of testing their consistency with EU law. In both of the Member States, indeed, there are several presumptions, either procedural (i.e. concerning the powers of control and assessment of the tax administration) or substantive (affecting directly the position of the taxpayer). Amongst these, there is a number of presumptive measures enacted in particular in the field of VAT (e.g. concerning the person liable to tax or the event giving raise to taxation) and Direct taxation (concerning cross-border situations: e.g. CFC rules, thin capitalization rules, transfer pricing rules, limitations to the deductibility of payments to low-tax States), some of which need to be evaluated in the light of EU law. The examination of the two national legal orders shows some differences. In the Italian system there has been an extensive debate concerning legal presumptions, due also to the numerous decisions of the Constitutional Court handed down on the matter, whereas so far there are few decision of the Belgian Constitutional Court. The overall approach to legal presumptions, however, is not different, and it shows how the parameter of evaluation is internal to the legal presumption itself, being the focus on the structure of the latter and on the consistency with the principle of reasonableness.

By contrast, at EU level the parameter is external, and is in turn embodied by the relevant EU right, principle or freedom at issue. The focus is on the effects of the legal presumption, and the latter is approved only in the extent to which it does not affect the regulation (for customs duties) or the model (for VAT and excise duties) designed at EU level or it is justified by an overriding reason in the public interest, but always on condition that such restrictions to the exercise of a EU right or freedom is proportionate to the aim attained. This results from the examination of the EU law context which is undertaken in the third chapter, and which pays particular attention to the case-law of the EUCJ in the domains of customs duties, VAT, direct taxation,

Finally, some conclusions are drawn, either with regard to the overall EU approach to legal presumptions compared to the national one and on the impact on the protection of the European taxpayer; or by testing some of the Italian and Belgian presumptive provisions that are suspect of not being in line with EU law.

Tax transparency: income allocation

PhD in law, defended on 1 July 2010 by Bart Peeters under the supervision of Bruno Peeters [in Dutch].

A study of the classification of cross-border cooperation

This research deals with the tax classification of commercial cooperation for the purposes of income tax. 'Cooperation' includes every possible form in which one or more individuals can jointly conduct a business activity, referred to using the broad term 'entity'. The classification allocates the income earned from a business activity to a taxpayer. If an entity is fiscally classified in a transparent manner, then the cooperating partners are taxed directly on the income earned. When classified as an independent taxpayer, the entity itself is taxed on the income earned. This classification may lead to additional taxation, since the cooperating partners may also be taxed when a separately taxed entity pays out a profit to them.

The first chapter examines the Belgian classification of foreign legal forms. Entities established under a foreign legal system often have special characteristics that differ from similar Belgian legal forms or sometimes have no comparable equivalent in Belgian law at all. Belgian tax classification, however, is implicitly based on the characteristics of Belgian legal forms. This may lead to difficult assessments, lacunas and discriminatory classifications for foreign entities. This chapter therefore proposes new classification criteria.

To this end, a two-part study was conducted. Firstly, the Belgian classification method was compared to the classification of (mainly foreign) legal forms in France, the Netherlands and the United States. Secondly, a more fundamental justification was sought for the classification of Belgian legal forms under Belgian tax law. A new classification method was thus derived, based on foreign classification methods but inspired by the Belgian situation.

The second chapter examines potentially conflicting simultaneous classifications of an entity in different tax law systems. Income derived via an entity established by cooperating partners may indeed be taxed in multiple states. A distinction is drawn between the source state of the income earned, the entity's state of establishment and the state of residence of each partner. Each state autonomously classifies the legal form that is to be used and who will be taxed under national tax law for the income earned. As regards both the source state of the income and the partners' state(s) of residence, this classification may be linked to an alien foreign legal form and the conclusions of Chapter 1 may affect the final classification. States that classify an entity as a single taxpayer may subsequently impose an additional tax on the cooperating partners if the (separately taxed) entity pays out the profits to the partners.

Whenever income is generated in a cross-border context, it is subject to various tax regimes. Thus, both the source state of the income and the state of residence of an income earner may tax this income, in theory. Most states have therefore drawn up bilateral tax treaties that reduce tax claims and divide the taxes between the two states. However, these treaties only regulate the distribution of the taxation powers, without focusing specifically on the allocation of income and the effects of different classification.

In the second part of this study, we look at how these bilateral treaties still implicitly restrict disproportionate taxation, despite the lack of a specific agreement. A general framework is derived and we establish which forms of excessive taxation remain after these treaties are applied. In particular, we focus on two treaties signed recently by Belgium, one with the Netherlands and the other with the United States. These treaties do indeed contain additional provisions that regulate global taxation in instances of conflicting classification, but it appears these provisions are not sufficiently clear.

Since each state decides individually which restrictions to national taxation are to be accepted in a treaty, this second part makes no general proposal regarding new treaty provisions. The study is limited to indicating individual discrepancies and how these can be eliminated if necessary.

'Agreements' with the tax authorities: limits, legal characterisation and legal consequences

PhD in law, defended on 26 June 2009 by Elly Van De Velde under the supervision of prof. dr. Bruno Peeters [in Dutch].


Worldwide, taxpayers are looking for legal certainty regarding the fiscal consequences of their actions. Worldwide, countries are trying to attract companies and (foreign) investors to boost their economies. Worldwide, people are longing for a change in mentality and more reciprocity in the relationship between the tax authorities and the taxpayer. For these reasons, tax authorities and taxpayers also consult each other worldwide. A legal system that can guarantee optimal fiscal predictability has significant advantages. In Belgium, too, the making of 'agreements' between the tax authorities and taxpayers is currently a popular daily practice. It sounds logical in the period when our tax returns are due.

 In Belgium, this concept is put into practice by means of a meeting organised by the legislator (according to the Law of 24 December 2002 regarding the Department of Preliminary Decisions in Tax Matters – the so-called Ruling Commission) or a kind of informal consultation between local tax officials and taxpayers. Such tax 'agreements' may theoretically relate to any tax (e.g. income tax, such as professional expenses or the distinction between other/professional income, corporate tax, VAT, registration and inheritance tax, transfer pricing issues), at any level of taxation (local, regional, federal, cross-border) and at all taxation stages over which the tax authorities preside (e.g. prior to a transaction, following a tax assessment, during a tax audit, during the litigation phase after an objection or even when the case is pending before the court).
In short, in each fiscal domain, both the formally organised and informal tax 'agreements' are considered effective means of offering taxpayers more legal certainty. But is this justified?

Despite the frequent use of this fiscal 'agreement' and the taxpayer's complete faith in this method, it appears from case-law that this instrument for obtaining legal certainty also causes legal uncertainty. What if the tax authorities reconsider an earlier 'agreement'? Where does that leave the taxpayer? In other words, what is the legal value of a tax 'agreement' and how binding is it? Is a fiscal 'agreement' legally enforceable or is it just a declaration of intent from the tax authorities? How can a tax 'agreement' be legally qualified? Does a so-called 'ruling' set any precedent? Can a third party use the ruling of another party? Can the tax authorities simply add conditions? What if an 'agreement' is against the law? Should the taxpayer have known this? Does the taxpayer have any legal protection in this case? Can he or she go to court to challenge (the refusal of) a ruling? If so, on what grounds? Members of the Belgian Parliament have recently begun to ask such questions, but the Belgian Minister of Finance has so far responded rather evasively. The taxpayer is not getting an answer to these essential and highly relevant questions regarding his or her legal status after making an 'agreement' with the tax authorities.

This doctoral research provides an answer to these topical and socially relevant questions, and subjects the practice of tax 'agreements' - which is likely to be a matter of concern for virtually every taxpayer at some point - to a critical legal analysis for the very first time. Previously, legal foundations for the practical superstructure had been lacking. The aim of the research was to map the legal limits, classification and consequences of 'agreements' made between the tax authorities and the taxpayer. This thesis is particularly relevant because the so-called Ruling Commission is currently evaluating its own operations and requesting suggestions for improvement from its clients, the taxpayers. This thesis can therefore provide a very well-argued contribution.

 Having explained the choice of the term 'agreement' and its concrete legal comparative interpretation, the thesis addresses the research question of whether and to what extent tax 'agreements' are permitted in Belgium. Like any other OECD and EU Member State, Belgium must respect supranational boundaries. One important boundary is the prohibition of fiscal state aid, which is closely monitored by the European Commission and the Court of Justice. In addition, the Belgian Constitution prescribes that no tax can be introduced except by law. This so-called fiscal principle of legality imposes a restrictive and essential limitation. Subsequently, we also examined the extent to which tax 'agreements' are permissible within the limits of the constitutional principle of equality and the one-year principle, the so-called public order nature of tax law and the general principles of good governance. This fundamental research delivered innovative, refreshing insights into a matter which is full of accepted truths. It was concluded that not all tax law is of concern to the public order and also that the distinction between 'agreements' on issues of law and fact is no longer tenable. The most important general conclusion was that the practice of tax 'agreements' is permissible, in principle, within a well-defined and limited legal framework.

 The second research question discusses the legal certainty of the tax 'agreement' itself. The purpose of the research was to formulate a theory which demonstrates the degree of legal certainty that can be assigned to the tax 'agreement'. Under current law, jurisprudence or legal doctrine, there is no consensus regarding the legal basis of the binding nature of tax 'agreements'. In order to guarantee the effectiveness of the measure and the legal protection of the taxpayer, it is nevertheless of paramount importance to determine the judicial qualification and associated legal consequences.
Having presented the current, diverse state of the law, an alternative, detailed, comprehensive vision of the legal classification of the tax 'agreement' (whether granted or denied) is provided for the first time. Based on the new legal classification, an answer is finally given to questions that are relevant to those working in the field regarding the contestability of this fiscal 'agreement', the competent jurisdiction, the extent of the jurisdiction of the judge and the applicable substantive law between the parties and regarding third parties.

This thesis therefore provides not only the legal theorist with an in-depth study of the fundamentals of the fiscal 'agreement', but also the legal practitioner with a socially relevant tool.

Congestion, transport taxes, and the labour market

PhD in Applied Economics, defended on 23 June 2009 by Bart Wuyts under the supervision of prof. dr. Bruno De Borger.

Essays on congestion, transport taxes and the labour market

It is no coincidence that political, social and scientific attention has recently turned to the issue of mobility. In recent decades, the demand for traffic has increased to such an extent that across the world, urban areas are struggling with heavy traffic and endless traffic jams.

The link between congestion and the labour market is obvious – congestion occurs mainly during the morning and evening commuting periods – but little research on this issue is visible in the scientific literature. This thesis examines various aspects of the complex relationship between congestion, transport taxes and the labour market.

The thesis first elaborates on the impact that free parking lots provided by employers have on the welfare effect of higher congestion taxes. It then examines the extent to which the structure of the labour market is relevant for the calculation of optimal transportation taxes. Next, a framework is set up in which employees receive not only monetary rewards, but perhaps also company cars. We investigate the effects of favourable taxation of company cars both on employment and on externality-cost policies. Finally, an econometric model is estimated, whereby wages and company cars depend on taxes and various employee and employer characteristics.

The various research topics are explained in more detail in the paragraphs below.

Parking spaces paid for by the employer
One of the main causes of current traffic problems is the fact that many employers provide commuters with a free parking space. Empirical studies (e.g. Shoup, 2005) have shown that when employees do not have to pay for the parking space they use, they are more likely to commute by car. Previous literature failed to examine the interaction between parking costs and the labour market, and Chapter 2 of this thesis therefore takes a detailed look at the impact of free parking spaces offered by employers on the welfare effects of increased congestion taxes. Firstly, it appears that a budget-neutral increase in congestion taxes (combined with lower income taxes or higher subsidies for public transport) leads to a more favourable welfare effect when taking into account the existence of free parking spaces. The reason is that congestion taxes not only correct congestion externalities, but also reduce the inefficiencies caused by the presence of free parking spaces. Secondly, it has been shown that the welfare benefits generated may be higher when the subsidies for public transport are increased than when taxes on labour are reduced. This result is explained by the very diverse effects that recycling instruments have on congestion. Finally, there appears to be a significant increase in welfare when employees are paid not to use a parking space.

Union negotiations or total competition: important or not?
The next chapter investigates whether the structure of the labour market is important for optimal transport policy. Intuitively, this seems to be true. If the labour market is competitive, the impact of congestion on employment will largely depend on how sensitive working opportunities are to higher commuting costs. However, if wages are determined by negotiations between employers and unions, then the effects of congestion and transport taxes on the labour market will largely be determined by the importance unions attach to employee mobility problems.

Chapter 3 deduces optimal congestion and labour taxes for a competitive labour market and various union negotiation models. The model provides for the possibility of working from home and both commuting and non-commuting employees are included. Several interesting results emerge. Firstly, we see that significant differences in optimal taxes arise depending on the assumed structure of the labour market. If the objective function of the union is based on the usefulness of the employees, and if the non-commuter traffic mainly consists of working households, then optimal congestion taxes appear to be higher in the competitive labour market than in the negotiation model. However, if the majority of non-commuter traffic consists of jobless households, we see the opposite: optimal congestion taxes are higher when wages are determined by negotiations than when the balanced wage is at the intersection of labour demand and supply.

A numerical illustration confirms the theoretical result described above. Moreover, when congestion taxes are differentiated between commuter and non-commuter taxes, we see a confirmation of the results produced by previous studies, which indicates that commuter traffic should be taxed at a lower rate than non-commuter traffic in a competitive labour market. In the negotiation model under consideration, the optimal congestion tax does not take into account the displacement motive.

Finally, we examine the role of working from home for optimal taxation, and find that the implementation of optimal taxation leads to a substantial increase in working from home. In line with expectations, working from home is stimulated more by uniform congestion taxes than by differentiated taxes. The numerical results indicate that if the efficiency of working from home is increased, optimal congestion taxes will be significantly lower.

Company cars and congestion taxes
In Belgium, a company car is part of the remuneration package for many employees. The very favourable tax treatment of company cars may play a role in this. Scientific literature has already suggested that the efficacy of transport policies aimed at reducing congestion depends on how company cars are taxed. Chapter 4 examines the relationship between congestion, the labour market and the fiscal treatment of company cars. The main conclusions are as follows. Regardless of company car taxation, both congestion and transport taxes have a negative impact on the presence of company cars. However, the further the commuting distance, the higher the likelihood of getting a company car. We also examine how preferential taxation of company cars affects welfare-optimal congestion and labour taxes, and we prove that low taxation of company cars gives rise to higher optimal congestion taxes. The reason is that low taxation of company cars is a direct cause of inefficiently high numbers of company cars, which lead to increased congestion and decreased use of public transport.

Company car as a form of remuneration
As mentioned above, company cars are gaining popularity as non-pecuniary compensation. To date, however, the literature has provided no framework in which the monetary wage, the possession and the value of a company car are the simultaneous results of negotiation between the profit of the firm and the preferences of the employee. Such an undertaking should take into account the impact of various costs on the company car decision. For example, if the employee does not receive a company car, he/she will be paid for all work-related journeys. If the employee does receive a company car, then the employer will pay a certain monthly lease amount (depending on the type of company car).

Chapter 5 explains the monetary wage and the amount that the employer pays for a company car. The model takes into account the favourable tax regime for company cars and the progressivity of income tax. At empirical level, an econometric analysis is conducted on the basis of a large survey carried out among Belgian employees. The econometric results suggest that tax rates have a significant positive effect on the share of the company car in overall remuneration. Furthermore, commuting distance was found to have a positive impact on both the monetary wage and the probability of a company car being provided. Contrary to the results provided in previous studies, we found a negative correlation between the size of the company and the likelihood that a company car is included in the remuneration.

The collection of taxes in cross-border situations

PhD in Law, defended on 29 September 2008 by Ilse De Troyer under the supervision of prof. dr. Bruno Peeters [in Dutch].

European integration has ensured that each of us can travel to and live in other European countries with relative ease. Tax fraudsters also make use of this freedom, however. Their taxes are left unpaid, and they move or transfer their assets to another country where our tax authorities cannot follow them. Tax officials do not have the power to act beyond their own borders. In other words, they cannot collect taxes in another country.

This phenomenon causes major problems for tax authorities. In the past, the government was able to arm itself against such defaulters by demanding predetermined guarantees. Under the influence of the European legislator and the European Court of Justice, however, these opportunities are becoming increasingly scarce. Free movement within Europe is considered sacred, and restrictions of that freedom are often seen as sacrilegious. For example, Belgium is no longer in a position to demand that foreign persons liable for VAT appoint a representative responsible for paying the VAT that is owed because of their activities. In addition, in the judgment of 9 November 2006, the Court of Justice condemned the Belgian rule that a client who relies on a contractor not registered in Belgium should withhold and transfer part of the invoice amount to the Belgian State as a guarantee for the taxes that a foreign contractor must pay here. According to the Court, this measure constituted an unlawful infringement of the freedom to provide services within the European Community.

In order to enforce tax payments in cross-border situations, mutual assistance in the recovery of tax is increasingly being sought. This means that the Belgian administration can ask the administration of another country to collect the Belgian taxes; similarly, the Belgian authorities respond to requests from international authorities to recover their taxes in Belgium.

However, this cooperation has not proven very successful. Of the total amount for which recovery assistance is requested, a maximum of only 5% has actually been collected as a result of intervention in another country. A major difficulty in this context is the complexity of the cooperation rules, which result from a multitude of treaties and regulations: the competent Belgian officials must find a way through the assistance provisions contained in about 40 double taxation treaties, a Benelux collection assistance treaty, two directives of the European Community, a treaty agreed upon by the Council of Europe and the OECD, and so on. In such a situation, it is difficult to see the wood for the trees. This thesis calls for a rationalisation, best carried out at European level.

From a practical point of view, there is a lot of room for improvement. For example, when the Belgian administration receives a request for collection assistance, it must often translate the attached enforceable title – based on which the collection takes place – to comply with the Belgian language laws. This thesis argues for the introduction of a uniform enforceable title. The use of a standard form would facilitate and expedite the work of the authorised departments.

The result of the collection assistance is ultimately dependent on the recovery options that exist in the state approached for help, and their willingness to act in the best interests of the requesting state. Countries that receive collection assistance should obviously be willing to provide it in return.

Permanent establishment in the new world: an outdated treaty notion

PhD in Law, defended on 27 September 2004 by Tim Wustenberghs under the supervision of prof. dr. Bruno Peeters [in Dutch].

Subtitle: The allocation of tax powers with regard to cross-border business profits: practice and theory.

The Belgian system of division of powers for taxation

PhD in Law, defended on 20 September 2004 by Nicole Plets under the supervision of prof. dr. Karel Rimanque [in Dutch].

The legal balancing act between member states' autonomy and the preservation of the internal economic union and monetary union in a federal state and more.

International transfer pricing

PhD in Applied Economics, defended on 3 September 2002 by Martine Cools under the supervision of prof. dr. Ann Jorissen and prof. dr. Clive Emmanuel (second supervisor, University of Glasgow).

Full title: International Transfer Pricing: Tensions between the tax requirements and the management control function of multinational enterprises

The redistributive effect of personal income taxes in Belgium

PhD in Applied Economics, defended on 2 May 2002 by Gerlinde Verbist under the supervision of prof. dr. Bruno De Borger.

Subtitle: An inquiry into the redistributive effect of personal income taxes in Belgium

The main contribution of this work lies in the development of the microsimulation model MISIM.

The fiscal treatment of the pricing of cross-border intra-group contracts.

PhD in Law, defended on 25 September 1997 by Patrick Cauwenbergh under the supervision of prof. dr. Bruno Peeters [in Dutch].

Positive and normative theory of budgetary decentralisation

PhD in Applied Economics, defended on 20 June 1986 by Jacques Vanneste under the supervision of prof. dr. Wim Moesen [in Dutch].

With applications in the municipal finances of Belgium.

The role and structure of taxation in Rwanda.

PhD in Law, defended on 21 November 1983 by Charles Kalinijabo under the supervision of prof. dr. J. J. Couturier [in French].