Information;Judgment — ECLI:EU:C:2024:500
Date: 2024-06-13
Language of the case: French
Court formation: Sixth Chamber
Subject matter: Free movement of workers;Fundamental rights;Charter of Fundamental Rights
Procedure: Reference for a preliminary ruling - inadmissible
Origin: Belgium

Summary C-380/23 – 1 
Case C-380/23 [Monmorieux] i  
Summary of the request for a preliminary ruling pursuant to Article 98(1) of 
the Rules of Procedure of the Court of Justice 
Date lodged:  
16 June 2023 
Referring court:  
Tribunal de première instance du Luxembourg (Belgium)  
Date of the decision to refer:  
14 June 2023 
Applicant:  
UN 
Defendant:  
État belge, represented by the Minister for Finance  
  
I. Facts and main proceedings: 
1 UN, a Belgian national, was domiciled in France, in the border area, and worked 
in Belgium, in the border area. Having claimed, for the 2008 to 2014 tax years, the 
specific tax regime for cross-border workers provided for in the Convention for 
the avoidance of double taxation between Belgium and France (‘the DTC’), he 
was taxed in France on income of Belgium origin. 
2 The Belgian tax authority took the view that UN had been wrong to claim 
eligibility for the special regime for the tax years concerned, since his only 
permanent residence was in Belgium. It had levied Belgian tax on the income 
earned during those tax years, adding a penalty of 50%. 
3 UN contests the automatic taxation of his income by Belgium and seeks to 
establish the liability of the Belgian State. On those two grounds, he referred the 
case to the tribunal de première instance (Court of First Instance, Belgium) on 
14 July 2016. At the same time, as a precautionary measure, he applied for the 
 
i The name of the present case is a fictitious name. It does not correspond to the real name of any party to the proceedings. 
EN 
SUMMARY OF THE REQUEST FOR A PRELIMINARY RULING – CASE C-380/23 
 
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mutual agreement procedure as provided for in Article 24 of the DTC, with a view 
to remedying the double taxation of his income. 
4 On 30 August 2017, the Belgian tax authority informed him of the decision taken 
by the Belgian and French tax authorities, in the following terms: 
‘Since the taxation by Belgium of that income for the years in question is 
recognised by both States as legitimate, the French tax authorities wish to 
proceed without undue delay with the rebate of the tax unduly collected by them 
on that income. 
However, to do that, it is essential that your client withdraws all administrative 
and judicial appeals against the Belgian taxes in question such that they became 
final. 
… 
I wish to draw your attention to the fact that in the event of refusal of that 
agreement and/or in the absence of withdrawal of all appeals, the Belgian and 
French authorities would be forced to terminate the mutual agreement procedure, 
with the aggravating circumstance of the risk of the double taxation being 
maintained on that income.’ 
5 By judgment of 13 March 2019, the Court of First Instance annulled the additional 
50% tax imposed for the 2008 to 2014 tax years and rejected the claim for the 
remainder, while reserving the right to rule on the liability action against the 
Belgian State. 
6 The Court of First Instance is now examining that liability action and refers the 
three questions set out below to the Court of Justice for a preliminary ruling. 
II. Legal framework 
Provisions of European Union law relied on 
7 Article 47 of the Charter of Fundamental Rights of the European Union (‘the 
Charter’) provides: 
‘Everyone whose rights and freedoms guaranteed by the law of the Union are 
violated has the right to an effective remedy before a tribunal in compliance with 
the conditions laid down in this Article. 
Everyone is entitled to a fair and public hearing within a reasonable time by an 
independent and impartial tribunal previously established by law. Everyone shall 
have the possibility of being advised, defended and represented. 
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Legal aid shall be made available to those who lack sufficient resources in so far 
as such aid is necessary to ensure effective access to justice.’ 
8 Article 45(1) TFEU provides: 
‘Freedom of movement for workers shall be secured within the Union.’ 
9 Lastly, Article 19(1) TEU provides: 
‘The Court of Justice of the European Union shall include the Court of Justice, the 
General Court and specialised courts. It shall ensure that in the interpretation and 
application of the Treaties the law is observed. 
Member States shall provide remedies sufficient to ensure effective legal 
protection in the fields covered by Union law.’ 
Convention between France and Belgium for the avoidance of double taxation 
10 Article 24(3) of the DTC provides: 
‘Where a resident of one of the Contracting States considers that taxes which have 
been or are to be assessed against him or her have resulted or will result in double 
taxation inconsistent with the provisions of the Convention, he or she may, 
without prejudice to the exercise of his or her rights of complaint and appeal under 
the domestic laws of either State, submit to the competent authorities of the State 
in which he or she is resident a written application, with a statement of grounds, 
for review of the said taxes. 
That application must be submitted within six months of the date of notification or 
collection at source of the second tax. If the application is upheld by the 
authorities to which it is submitted, those authorities shall come to an agreement 
with the competent authorities of the other Contracting State with a view to the 
avoidance of double taxation.’ 
III. The essential arguments of the parties in the main proceedings 
1. Position of the applicant 
11 UN submits that the Belgian State is infringing his rights of defence and his 
fundamental rights by forcing him to choose between pursuing his action before 
the Belgian courts and being eligible for the mutual agreement procedure, in this 
case the restitution of the French tax paid for the tax years at issue. 
12 In his view, the institution of a mutual agreement procedure is without prejudice 
to the taxpayer’s domestic rights of appeal. The Belgian State is depriving him of 
his fundamental right to submit fully and freely to the courts the dispute between 
him and the tax authority, even though the tax authorities of the two States 
SUMMARY OF THE REQUEST FOR A PRELIMINARY RULING – CASE C-380/23 
 
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recognise that double taxation exists contrary to the DTC. UN argues that he has 
incurred significant administrative penalties which are of a coercive nature and 
claims that the choice left to him infringes his rights of defence. 
13 UN also considers that the fact of terminating the mutual agreement procedure 
without allowing him to submit observations and without awaiting the outcome of 
the judicial proceedings constitutes a violation of his rights of defence and of 
Article 6 of the European Convention on Human Rights and Fundamental 
Freedoms. The resulting loss he incurs is equal to the amount of tax paid in 
France, which the mutual agreement procedure causes him to forfeit permanently. 
UN also notes that, according to Article 13 of the Belgian Constitution, ‘no one 
can be separated, against his will, from the judge that the law has assigned to 
him’. 
2. Position of the Belgian State 
14 The Belgian State recalls that the mutual agreement procedure provided for by the 
DTC allows the taxpayer to request that the Belgian and French tax authorities 
enter into a direct dialogue to find a solution to the double taxation. This is not a 
mandatory phase for the taxpayer or an appeal within the meaning of the Code 
judiciaire (Judicial Code). 
15 The words ‘without prejudice to the exercise of his rights of complaint and appeal 
under the domestic laws of either State’ in the DTC simply mean that this 
procedure does not affect the taxpayer’s right to lodge a complaint and right of 
appeal under the domestic laws of each country. The mutual agreement procedure 
is independent of the remedies available under the national laws of the States. 
16 Moreover, bringing a legal action against taxes established in Belgium has no 
suspensory effect on the continuation of the mutual agreement procedure. The 
litigation procedure, in which the taxpayer plays an active role, takes place as 
provided for by the Code des impôts sur les revenus 1992 (Income Tax Code 
1992) and the Judicial Code, whereas the mutual agreement procedure provided 
for by the DTC takes place between two States; in principle the taxpayer is not 
involved in discussions between the competent authorities. In the present case, a 
solution to avoid double taxation has been found and the Belgian tax authority has 
informed the taxpayer, specifying that the enforcement of the agreement is subject 
to his withdrawal of any domestic litigation proceedings: this practice seeks to 
avoid any conflict between the outcome of the domestic procedure and that of the 
mutual agreement procedure, and is unobjectionable according to recent domestic 
case-law. The OECD also permits it, since in its commentary on Article 25 of the 
Model Tax Convention it states that: ‘45. … there may be a pending suit by the 
taxpayer on an issue, or else the taxpayer may have preserved the right to take 
such domestic law action, yet the competent authorities might still consider that an 
agreement can be reached. In such cases, it is, however, necessary to take into 
account the concern of a particular competent authority to avoid any divergences 
or contradictions between the decision of the court and the mutual agreement that 
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is being sought, with the difficulties or risks of abuse that these could entail. In 
short, therefore, the implementation of such a mutual agreement should normally 
be made subject: 
– to the acceptance of such mutual agreement by the taxpayer, and 
– to the taxpayer’s withdrawal of the suit at law concerning those points settled in 
the mutual agreement’ (OECD, Model Tax Convention on Income and on 
Capital: Condensed Version 2014, OECD Publishing, p. 414). 
VI. Succinct presentation of the reasoning in the request for a preliminary 
ruling 
17 The question that arises in the present case is whether the enforcement of the 
amicable settlement reached with the French tax authority (the restitution of 
French tax) can be contingent on the taxpayer’s unconditional withdrawal of his 
legal action in Belgium. 
18 The referring court holds that it is not unlawful for a person who is automatically 
taxed in Belgium after having paid income tax in France to challenge that taxation 
before the Belgian court. Indeed, the income tax claimed in Belgium will 
generally be four or even five times higher than the French tax calculated on the 
same income, and that basic tax, which is much higher, will be further increased 
by penalties of 50% of the tax claimed. 
19 Moreover, although the applicant is requesting that the Contracting States consult 
each other under the mutual agreement procedure provided for in Article 24 of the 
DTC, it is primarily for the purpose of ending the double taxation. 
20 The referring court is uncertain whether the Belgian State is complying with 
Articles 19 TEU, 45 TFEU and Article 47 of the Charter when it makes the 
restitution of French tax contingent on the withdrawal of the application brought 
before the Belgian court under the provisions of the DTC and domestic law, 
whereas, according to the fixed policy of the Belgian tax authority, the taxpayer 
does not have access to the administrative documents relating to the mutual 
agreement procedure and, in any event, cannot determine whether his tax situation 
has actually been examined by the tax authorities of the two Contracting States. 
21 The referring court notes that the Commission d’accès aux documents 
administratifs (Committee on Access to Administrative Documents) takes the 
view that the refusal of the tax authorities to grant access to the file when a request 
for access to documents relating to a mutual agreement procedure on the basis of a 
double taxation convention is addressed to it is contrary to Article 32 of the 
Constitution and Articles 4 and 6 of the loi du 11 avril 1994 relative à la publicité 
de l’administration (law of 11 April 1994 on disclosure of information by the 
administration). 
SUMMARY OF THE REQUEST FOR A PRELIMINARY RULING – CASE C-380/23 
 
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22 The referring court considers that the dispute concerns the free movement of 
workers, since UN submitted that he resided in France and paid income tax there. 
As a reminder, it has been consistently held that, whilst direct taxation falls within 
their competence, the Member States must nonetheless exercise that competence 
consistently with European Union law. 1 Thus, although the Member States are at 
liberty, in the framework of bilateral agreements for the avoidance of double 
taxation, to determine the connecting factors for the purposes of allocating powers 
of taxation, that allocation of powers of taxation does not allow them to apply 
measures that are contrary to the freedoms of movement guaranteed by the Treaty. 
As far as concerns the exercise of the power of taxation thus allocated, the 
Member States must comply with EU rules. 2 Therefore, where they are bound by 
bilateral conventions for the avoidance of double taxation, Member States are 
obliged to respect the general principles of EU law and the fundamental rights of 
EU citizens. 
23 The referring court recalls that Article 47 of the Charter, which constitutes a 
reaffirmation of the principle of effective judicial protection, enshrines the right to 
an effective remedy before a tribunal for every person whose rights and freedoms 
guaranteed by Union law are infringed. 3 
24 It follows that in certain cases, where there is evidence that both supports and 
undermines the applicant’s case, the applicant may be justified in seeking to 
convince a court of the substance of his or her argument while retaining a 
legitimate interest in recovering the foreign tax should it not be examined by the 
court. 
25 Added to this is the fact that taxation in Belgium is accompanied by penalties for 
fraud (intention to avoid taxation), increasing the taxation from 50% to 200%, 
which Article 6 of the European Convention on Human Rights has long defined as 
criminal. However, the Cour constitutionnelle (Constitutional Court, Belgium) 
and the Cour de Cassation (Court of Cassation, Belgium) have recognised that the 
Belgian taxpayer has the right to apply to the court for a review of the 
proportionality of the administrative penalty of a coercive nature and to be eligible 
for suspension. The principle of proportionality, as a general principle of EU law, 
requires Member States to employ means which, while enabling them effectively 
to attain the objective pursued by national legislation, cause the least possible 
 
1 See, to that effect, judgment of 23 January 2014, Commission v Belgium (C-296/12, 
EU:C:2014:24, paragraph 27 and the case-law cited). 
2 See, to that effect, judgments of 14 March 2019, Jacob and Lennertz (C-174/18, 
EU:C:2019:205, paragraph 25 and the case-law cited), and of 24 October 2019, État belge 
(C-35/19, EU:C:2019:894). 
3 Judgments of 27 June 2013, Agrokonsulting-04 (C-93/12, EU:C:2013:432, paragraph 59), and 
of 2 March 2021, A.B. and Others (Appointment of judges to the Supreme Court – Appeal) 
(C-824/18, EU:C:2021:153, paragraph 87 and the case-law cited). 
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detriment to the principles laid down by EU legislation. 4 However, in the present 
case, there is no risk of double non-taxation if the tax authorities of the two States 
suspend the examination of the applicant’s situation under the mutual agreement 
procedure until the national judicial proceedings lead to a final decision by the 
Belgian courts, so as not to deprive the applicant of the restitution of the French 
tax. 
V. Questions referred for a preliminary ruling 
26 The referring court therefore requests the Court of Justice of the European Union 
to answer the following questions by a preliminary ruling: 
‘1. Does Article 24 of the Convention between France and Belgium for the 
avoidance of double taxation and the establishment of rules of reciprocal 
administrative and legal assistance with respect to taxes on income, signed at 
Brussels on 10 March 1964, ratified by the law of 14 April 1965, interpreted as 
meaning that a Belgian citizen who claims to be resident for tax purposes in 
France – which is, however, contested by the Belgian tax authority – and who, as 
a precautionary measure, has applied for the mutual agreement procedure in order 
to recover the tax paid in France, who is required by the Belgian and French tax 
authorities, in order to have the right to the restitution of that tax, to withdraw 
unconditionally the judicial proceedings brought before the Belgian courts 
principally to challenge his being automatically taxed in Belgium, infringe 
Article 19 of the Treaty on the European Union, Article 45 of the Treaty on the 
Functioning of the European Union and Article 47 of the Charter of Fundamental 
Rights of the European Union, in conjunction with the principle of 
proportionality, in so far as he or she would permanently forfeit the right to the 
restitution of French tax if he or she were to pursue his or her principal challenge 
to being taxed in Belgium before the Belgian ordinary court? 
2. If the answer to the first question is in the negative, does the answer remain 
the same if, in order to recover the tax paid in France, the applicant, by 
withdrawing his or her legal action challenging the taxation in Belgium, also loses 
the right to an effective judicial review of the administrative penalties of a 
coercive nature, which the European Convention on Human Rights defines as 
criminal and which increase the amount of tax, thereby losing the right to review 
the proportionality of the penalty and apply for a suspension, modes of 
customising the penalty that are recognised by both the Constitutional Court and 
the Court of Cassation? 
 
4  See, to that effect, judgments of 8 February 2018, Lloyd’s of London (C-144/17, EU:C:2018:78, 
paragraph 32 and the case-law cited); of 14 October 2021, Finanzamt N and Finanzamt G 
(Communication of the allocation decision) (C-45/20 and C-46/20, EU:C:2021:852, paragraph 
62 and the case-law cited); of 8 December 2022, BTA Baltic Insurance Company (C-769/21, 
EU:C:2022:973); and of 22 December 2022, Shell Deutschland Oil (C-553/21, 
EU:C:2022:1030). 
SUMMARY OF THE REQUEST FOR A PRELIMINARY RULING – CASE C-380/23 
 
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3. If the answer to the first two questions is in the negative, does the answer 
remain the same if there is an administrative policy whereby the applicant is 
refused access to documents relating to the mutual agreement procedure between 
the two Contracting States, which refusal has repeatedly been deemed contrary to 
Article 32 of the Constitution and Articles 4 and 6 of the law of 11 April 1994 on 
disclosure of information by the administration by the Commission for Access to 
Administrative Documents and by the Conseil d’État (Council of State, 
Belgium)?’