A1 Certificate Fraud: Key Takeaways from the 2025 ECJ Decision

In a landmark judgement issued on January 23, 2025 (Case C-421/23), the European Court of Justice (ECJ) provided important clarifications on the application of EU social security regulations concerning posted workers and the authenticity of A1 certificates.

While the judgment was delivered earlier this year, its practical implications are coming into sharper focus now as national authorities begin to operationalise the ECJ's guidance—particularly in the context of increasing cross-border inspections and enforcement activity. The case offers timely and important guidance on the obligations of national authorities and courts in the presence of fraudulent A1 certificates.

This blog outlines the main takeaways from the decision and how the ECJ ruling impacts Employers requesting A1 Certificates in the EU.

What is an A1 Certificate and why does it matter?

An A1 Certificate is a document issued by a competent national social security authority that evidences where the employee’s social security contributions are being paid. It applies to posted workers, business travellers, and self-employed workers on temporary assignments and to workers that perform duties in multiple EU countries at the same time.

The A1 Certificate helps ensure legal compliance, avoid double social security payments, and is often required for immigration and posted worker notifications. Failure to secure an A1 Certificate may lead to high fines or delays in work approvals. 

What was the 2025 ECJ case about?

Case C-421/23 originated from criminal proceedings in Belgium against a Portuguese contractor who had employed 650 Portuguese workers on Belgian construction sites between 2012 and 2017. The employees were in possession of A1 certificates that had not been issued by the competent Portuguese social security institution.

As the Belgian social security authorities discovered that the A1 certificates were fraudulent, the Belgian court found the Portuguese employer guilty of fraud in relation to social security contribution payments and the use of false documents. The case was subsequently brought in front of the Court of Appeal, which referred some important questions to the ECJ.

Overview of the ECJ Ruling in Case C-421/23 

The ECJ made three key findings:

• • • Regulation 883/2004 on the coordination of social security systems applies even when A1 certificates are found to be fraudulently obtained, because it ensures that employees are subject only to one EU member State’s social security legislation at the time, which prevents legal uncertainty. Consequently, national courts must assess whether the conditions for posting workers from a social security perspective have been met in accordance with the posting provisions of the Regulation.
    • When there is a suspicion of fraud, national authorities of the member States mandatorily must engage in the structured dialogue and conciliation procedure laid down in Regulation 883/2004 before making a unilateral finding of fraud, which re-affirms one of the important principles of social security coordination, i.e. the principle of sincere cooperation between member States.
    • When the issuing social security authority explicitly denies having issued the A1 certificates (or confirms they are invalid), the national courts of the other member State are no longer bound by their contents, without the need for any further administrative consultation.

What this means for businesses operating in multiple EU countries

The ECJ ruling in reference reinforces the importance of A1 certificates in the field of labor migration and intra-EU employee mobility. A1 certificates hold significant legal weight, and host country inspection authorities cannot simply disregard them or impose social security contributions—even in cases where the certificates are suspected or found to be fraudulent.

Importantly, the ruling re-confirms the importance of legal certainty and ‘strong’ validity of an A1 by highlighting the mandatory nature of the dialogue and conciliation procedure between national authorities of different Member States. A1 certificates safeguard companies from host country social security claims, and in cases of doubt, host authorities are required to initiate the conciliation procedure with the home Member State before any withdrawal or challenge of the A1 form—ensuring that companies are not exposed to double social security contributions.

This case re-enforces the tendency we have seen over the last years in the increase in inspections across European countries regarding the absence of A1 Certificates for posted workers and it emphasises the importance of compliance with social security obligations when posting employees. To facilitate this enforcement, the EU has now fully implemented systems such as the Electronic Exchange of Social Security Information (EESSI), a digital platform that connects social security institutions across the EU. With this the European Union is trying to streamline the verification process and cooperation among national authorities.

How can Fragomen help?

The Fragomen Social Security team assist clients in managing their A1 certificate applications in line with EU regulations. With a strategic focus on compliance, the team helps ensure that social security, immigration, and posted worker obligations are considered early in the planning process.

Need to know more?

For questions regarding A1 compliance, please contact the Fragomen Social Security team at [email protected].

This blog was published on 28 May 2025, and due to the circumstances, there are frequent changes. To keep up to date with all the latest updates on global immigration, please subscribe to our alerts and follow us on LinkedIn, Twitter, Facebook and Instagram.