Judgment of the Court (Seventh Chamber) of 23 January 2025.Ministère public and Office National de Sécurité Sociale (ONSS) v EX.Reference for a preliminary ruling – Migrant workers – Social security – Applicable legislation – Posted workers – Documents in the form of A1 certificates allegedly issued by the institution competent to issue those certificates – Regulation (EC) No 883/2004 – Article 76(6) – Obligation of the authorities of the host Member State to initiate a dialogue and conciliation procedure for the purpose of determining whether fraud has occurred.Case C-421/23.

This judgment concerns the interpretation of EU social security coordination rules in cases of suspected fraud with A1 certificates for posted workers. The key points are:The essence of the act in 3-5 sentences:
The Court ruled on whether EU social security coordination rules apply when false A1 certificates are used for posted workers, and whether a mandatory dialogue procedure between Member States is required before establishing fraud. The case involved a Portuguese contractor who posted workers to Belgium using allegedly false A1 certificates. The Court confirmed that EU rules apply even when certificates are found to be false, and that dialogue between Member States’ institutions is mandatory before courts can make final determinations about fraud.Structure and main provisions:
– The judgment addresses three key questions about application of Regulation 883/2004 to cases with false A1 certificates
– It confirms that EU social security coordination rules apply even when certificates are proven false
– It establishes that the dialogue and conciliation procedure between Member States is mandatory before courts can make final fraud determinations
– It sets out specific requirements for when courts can disregard A1 certificates and find fraudMost important provisions:
1. EU social security coordination rules apply even when false A1 certificates are used
2. Member States must follow mandatory dialogue procedures before courts can make fraud determinations
3. Courts can only disregard A1 certificates after proper dialogue between national institutions confirms they are false
4. When social security contributions were collected, fraud can only be established after institutions determine which country’s laws should have applied

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