Judgment;Summary — ECLI:EU:C:2025:36
Date: 2025-01-23
Language of the case: French
Court formation: Seventh Chamber
Subject matter: Social security for migrant workers
Procedure: Reference for a preliminary ruling
Origin: Belgium

Anonymised version 
Translation C-421/23 – 1 
Case C-421/23 
Request for a preliminary ruling 
Date lodged: 
10 July 2023 
Referring court: 
Cour d’appel de Liège (Belgium) 
Date of the decision to refer: 
25 May 2023 
Appellant: 
Ministère public 
Civil party: 
Office National de Sécurité Sociale (ONSS) 
Accused person: 
EX 
  
[…] 
Cour d’appel de Liège (Court of Appeal, Liège, Belgium) 
Judgment 
delivered by the SIXTH Criminal Division 
IN THE CASE OF: 
MINISTÈRE PUBLIC (Public Prosecution Service, Belgium) 
AND 
EN 
REQUEST FOR A PRELIMINARY RULING OF 25. 5. 2023 – CASE C-421/23 
 
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ONSS (National Social Security Office, Belgium) […] 
- civil party and voluntary intervener 
[…] 
v 
[EX], […] of Portuguese nationality, without a known address in Belgium, 
formerly residing at […] Barcelos (PORTUGAL), declares that he currently 
resides […] at 4490 PÓVOA DE VARZIM (PORTUGAL) 
- accused person 
present and represented by Steve LAMBERT, lawyer in BRUSSELS 
Charged with: 
[…] 
A. […]. [Charge not covered by the notice of appeal] 
B. […]. [Charge not covered by the notice of appeal] 
C. Non-payment of social security contributions following a refusal to file a 
declaration 
In [his] capacity as employer or agent: 
[…] 
Having paid less in contributions than the amount he is liable for, or having failed 
to pay contributions following an omission or refusal to file a declaration or to 
provide the information referred to in paragraph 2, or an act provided for in 
Articles 232 and 235. 
Between 31 January 2012 and 31 January 2018, having failed to pay, as employer 
or agent, the contributions due in respect of the employment of staff effectively 
employed in Belgium on behalf of the 10th and 11th accused persons, that is to 
say the 640 workers who were fraudulently posted from Portugal to Belgium. 
[…] 
D. […]. [Charge not covered by the notice of appeal] 
E. Swindling under social criminal law 
[…] 
In the present case, […] 
ONSS 
 
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[…] 
-  having used forged posting forms and forged posting agreements with a 
view to carrying out fraudulent postings of workers from the companies in order 
to give the appearance of legality to the postings of workers, and forged invoices 
in order to conceal the fraudulent nature of the posting; 
[…] 
F. […]  
[…] 
[…] [Charge not covered by the notice of appeal] 
G. […] 
[…]  
[…] [Charge not covered by the notice of appeal] 
H. Money laundering (related) 
[…] 
Having converted or transferred the property referred to in Article 42(3) of the 
Code pénal (Belgian Criminal Code), for the purpose of concealing or disguising 
the illicit origin of the property or of assisting any person who is involved in the 
commission of the offence from which that property derives to evade the legal 
consequences of his actions. 
Having concealed or disguised the true nature, source, location, disposition, 
movement or ownership of the property referred to in Article 42(3) of the Belgian 
Criminal Code, when they knew or ought to have known the origin. 
*************** 
Having regard to the judgment delivered on 10 November 2021 (Order No 989) 
by the tribunal de première instance de NAMUR (Court of First Instance, Namur, 
Belgium), NAMUR division, which: 
IN THE CRIMINAL PROCEEDINGS: 
UPHOLDS the charges A, B, C, D.1, D.2, D.3, E, F, G.1 and H, as worded; 
SENTENCES the accused person: 
- to a term of imprisonment of four YEARS and a fine of EUR 100 000 x 6, 
and therefore a total of EUR 600 000, or an additional three months’ 
REQUEST FOR A PRELIMINARY RULING OF 25. 5. 2023 – CASE C-421/23 
 
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imprisonment, suspended for five years for half of the term of 
imprisonment and of the fine; 
- […] [additional penalties, not relevant to the questions referred for a 
preliminary ruling] 
HEREBY ORDERS: 
- the confiscation of the sum of EUR 15 461 997.38. 
and orders such sum to be awarded to the ONSS. 
- […] [other confiscations, not relevant to the questions referred for a 
preliminary ruling] 
IN THE CIVIL PROCEEDINGS: 
[…] 
The application of the ONSS to join the criminal proceedings as a civil party is 
admissible and well-founded for the provisional amount of EUR 15 978 913.72. 
[…] 
*************** 
[…] 
FOLLOWING DELIBERATIONS 
1. Procedure 
The appeals of the accused person [EX] and those of the Belgian Public 
Prosecution Service against the accused person are admissible since they were 
submitted in the form and within the time limit prescribed by law. 
The accused person contests his guilt in respect of charges C, E and H, the level of 
the sentence and the orders for payment of damages. 
The prosecution objects to the level of the sentence. 
2. Assessment 
Facts 
The Court of First Instance, Namur, has accurately set out the facts of the case. 
It is sufficient for the Court of Appeal, Liège, to note that the accused person was 
proved to have employed, through Belgian, Portuguese, English and Luxembourg 
ONSS 
 
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companies, 650 workers of Portuguese nationality in the construction sector in 
Belgium. 
Only charges C (non-payment of social security contributions), E (swindling 
under social criminal law) and H (money laundering) are contested before the 
Court of Appeal, Liège. It therefore observes that Portuguese workers were posted 
to Belgium during the years 2011 to 2017, under cover of forged A1 certificates, 
to be employed on construction sites in Belgium. 
The Court of First Instance, Namur, held that the A1 certificates and the posting 
agreements – covered by charges D1 and D2, not challenged before the court – 
were forgeries. 
However, posting certificates must be requested from the Portuguese social 
security authorities and issued by them to allow the workers covered by those 
certificates to remain subject to social security in their country of origin. 
In addition, for those workers to be posted to another EU Member State, the 
employer must have a substantial activity in the State in which it is established. 
Moreover, the maximum duration of the posting is 24 months. 
Substance 
In the first ground of appeal, the accused person submits that, as soon as the 
competent institution of the host Member State raises doubts as to the accuracy of 
the facts on the basis of which the A1 certificates were issued, it is for the 
competent social security institution of the Member State that issued those 
certificates to assess their merits. 
It is established that as long as an A1 certificate is not withdrawn or declared 
invalid, the competent institution of the Member State in which an employee 
actually works must take account of the fact that that person is already subject to 
the social security legislation of the Member State in which the undertaking 
employing him is established, and that institution cannot therefore subject the 
worker in question to its own social security system. 1 
The Court of Justice of the European Union notes that it follows from the 
principle of sincere cooperation that every institution of a Member State must 
carry out a proper assessment of the application of its own social security regime. 
It also follows from this principle that institutions of the other Member States are 
entitled to expect that the institution of the Member State concerned fulfils that 
obligation. 2 
 
1 Judgment of 27 April 2017, A-Rosa Flussschiff (C-620/15, EU:C:2017:309, paragraph 43 and 
the case-law cited). 
2 See, by analogy, judgment of 3 March 2016, Commission v Malta (C-12/14, EU:C:2016:135, 
paragraph 37). 
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As a result, it is incumbent on the competent institution of the Member State 
which issued the A1 certificate to reconsider the grounds for its issue and, if 
appropriate, to withdraw the certificate if the competent institution of the Member 
State in which the employee actually works expresses doubts as to the accuracy of 
the facts on which the certificate is based and, consequently, of the information 
contained therein, in particular because that information does not meet the 
requirements of Article 14(1)(a) of Regulation No 1408/71 (now Regulation 
No 883/2004). 3 
Article 5 of Regulation (EC) No 987/2009 of the European Parliament and of the 
Council of 16 September 2009 laying down the procedure for implementing 
Regulation (EC) No 883/2004 on the coordination of social security systems states 
that: 
‘1. Documents issued by the institution of a Member State and showing the 
position of a person for the purposes of the application of the basic Regulation and 
of the implementing Regulation, and supporting evidence on the basis of which 
the documents have been issued, shall be accepted by the institutions of the other 
Member States for as long as they have not been withdrawn or declared to be 
invalid by the Member State in which they were issued. 
2. Where there is doubt about the validity of a document or the accuracy of the 
facts on which the particulars contained therein are based, the institution of the 
Member State that receives the document shall ask the issuing institution for the 
necessary clarification and, where appropriate, the withdrawal of that document. 
The issuing institution shall reconsider the grounds for issuing the document and, 
if necessary, withdraw it.’ 
By that certificate, the competent institution of the Member State in which an 
undertaking employing the workers concerned is established declares that its own 
social security system remains applicable to those workers. As previously 
mentioned, by virtue of the principle that workers must be covered by only one 
social security system, the certificate thus necessarily implies that another 
Member State’s social security system cannot apply. 4 
In the present case, no A1 certificate was issued by the Portuguese social security 
institutions, since the Court of First Instance, Namur, established that those 
certificates were forgeries. 
However, the accused person submits that where there is evidence of fraud – a 
hypothesis that must include the case of forged A1 certificates which do not 
originate from the authority competent to issue them – the dialogue and 
conciliation procedure must nevertheless take place. He argues that it is an 
 
3 Judgment of 6 February 2018, Altun and Others (C-359/16, EU:C:2018:63, paragraph 43). 
4 Judgments of 26 January 2006, Herbosch Kiere (C-2/05, EU:C:2006:69, paragraph 21), and of 
27 April 2017, A-Rosa Flussschiff (C-620/15, EU:C:2017:309, paragraph 38). 
ONSS 
 
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essential prerequisite for determining whether the conditions for the existence of a 
fraud are met. 
In examining this ground of appeal, the Court of Appeal, Liège, notes at the outset 
that Regulation No 987/2009 codified the case-law of the Court of Justice, 
affirming the binding nature of the A1 certificate and the exclusive competence of 
the issuing institution to assess the validity of that certificate, and expressly 
reproducing the abovementioned procedure as a means of resolving disputes 
concerning both the accuracy of documents drawn up by the competent institution 
of a Member State and determining the legislation applicable to the worker 
concerned. 5 
However, such considerations must not result in individuals being able to rely on 
EU law for abusive or fraudulent ends. 
Indeed, the principle of prohibition of fraud and abuse of rights is a general 
principle of EU law which individuals must comply with. Accordingly, the 
application of EU legislation cannot be extended to cover transactions carried out 
for the purpose of fraudulently or wrongfully obtaining advantages provided for 
by EU law. 6 
The Court of Appeal, Liège, observes that, especially in the context of suspicion 
of fraud, the implementation of the dialogue and conciliation procedure, prior to 
any final finding of fraud by the competent authorities of the host Member State, 
is of particular importance, since that procedure is such as to permit the competent 
institution of the issuing Member State and that of the host Member State to 
engage in dialogue and to cooperate closely in order to check and ingather, using 
the investigatory powers available to them under national law, all relevant matters 
of fact or law that may dispel or, on the contrary, confirm the accuracy of, the 
doubts expressed by the competent institution of the host Member State 
concerning the circumstances surrounding the issue of the A1 certificates which, 
in the present case, are considered to be forged. 7 
According to the case-law of the Court of Justice, that procedure constitutes an 
essential prerequisite for determining whether the conditions for the existence of a 
fraud are met and therefore, for taking all appropriate action as to the validity or 
otherwise of the A1 certificates at issue and as to which social security legislation 
is applicable to the workers concerned. 8 
 
5 Judgment of 27 April 2017, A-Rosa Flussschiff (C-620/15, EU:C:2017:309, paragraph 59). 
6 See judgments of 5 July 2007, Kofoed (C-321/05, EU:C:2007:408, paragraph 38), and of 
22 November 2017, Cussens and Others (C-251/16, EU:C:2017:881, paragraph 27). 
7 Judgment of 2 April 2020, CRPNPAC and Vueling Airlines (C-370/17 and C-37/18, 
EU:C:2020:260, paragraph 66). 
8 Judgment of 2 April 2020, CRPNPAC and Vueling Airlines (C-370/17 and C-37/18, 
EU:C:2020:260, paragraph 71). 
REQUEST FOR A PRELIMINARY RULING OF 25. 5. 2023 – CASE C-421/23 
 
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The Court of Justice appears to consider the dialogue and conciliation procedure 
to be an essential prerequisite, given the risk of undermining the principle that 
persons are to be subject to the legislation of a single Member State, the risk of 
double contributions, and the risk of jeopardising the dialogue and conciliation 
procedure which is based on sincere cooperation between the competent 
institutions of the Member States. 
In the present case, although concrete evidence of fraud exists and was established 
and accepted by the Court of First Instance, Namur, it should also be noted that 
social security contributions were actually paid to the Portuguese social security 
authority without the Court of Appeal, Liège, being informed of the reasons for 
those payments, since both the prosecution and the civil party submit that the 
relevant companies were never active in Portugal. 
Moreover, that fact is likely to have an impact on any confiscations ordered, 
where appropriate, by the Court of Appeal, Liège, if the charges before it were to 
be upheld. 
In those circumstances, the Court of Appeal, Liège, considers it necessary to refer 
the questions set out in the operative part of this judgment to the Court of Justice 
of the European Union for a preliminary ruling. 
ON THOSE GROUNDS, 
[…] 
The Court, 
Before giving judgment on the substance of the case, rules that it is necessary to 
refer the following questions to the Court of Justice of the European Union for a 
preliminary ruling: 
1. Is Regulation No 883/2004 of the European Parliament and of the 
Council of 29 April 2004 on the coordination of social security 
systems to be interpreted as applying in a situation where it has been 
held, without the point being contested by the parties, that, first, the A1 
certificates produced are forged according to the judicial authorities of 
the host State and, second, the investigations duly carried out by the 
judicial authorities of that host State appear to show that the 
certificates at issue were not issued by the competent authority of the 
issuing State, even though social security contributions have been paid 
to that authority? 
2. If the answer to the previous question is in the affirmative, is the 
dialogue and conciliation procedure established by Article 76(6) of 
Regulation No 883/2004 9 (which reproduces the procedure provided 
 
9 […]. [Footnote placed in parentheses in the main body of the question] 
ONSS 
 
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for in Article 84a(3) of Regulation No 1408/71) an essential 
prerequisite for determining whether the conditions for the existence of 
a fraud are met? 
3. If the answers to the previous two questions are in the affirmative, in 
accordance with the principle of prohibition of fraud and abuse of 
rights, which is a general principle of EU law which individuals must 
comply with, may the authorities of the State in which the employees 
exercised their activity disregard the abovementioned A1 certificates, 
including in the absence of recourse to the dialogue and conciliation 
procedure in the event of suspicion of fraud, where the facts submitted 
for assessment by them support the conclusion that those certificates 
were produced as a result of conduct on the part of the employer which 
a judicial authority of the host State found to be fraudulent? 
Reserves judgment as to the remainder and suspends the case sine die. 
[…] 
Delivered […] on 25 May 2023 […] [Signatures and standard wording]