The A1 Certificate: The Employer’s Guide
What it proves, who issues it, how long it lasts, and why French authorities are bound by it — including the exact limits the Court of Justice has drawn. Sourced from Regulations 883/2004 and 987/2009 and the CJEU.
One worker, one scheme: what the A1 certifies
EU social security coordination rests on a simple principle set by article 11 of Regulation (EC) 883/2004: a worker is subject to one member state’s social security legislation at a time. The A1 portable document certifies which one — and therefore where contributions are due.
Two situations dominate in practice: the posted worker who temporarily works in France while staying affiliated at home (article 12), and the multi-state worker who habitually works in several countries (article 13). The A1 covers both — but the rules, criteria and competent institutions differ.
Posting: home affiliation for up to 24 months
Under article 12 of Regulation 883/2004, a worker posted to France can remain affiliated to the sending state’s scheme for a posting of up to twenty-four months, provided the conditions detailed by article 14 of Regulation (EC) 987/2009 are met — including that the worker is not sent to replace another posted person. The A1 is issued before departure by the competent institution of the sending state.
Longer situations are not automatically excluded: article 16 of Regulation 883/2004 lets the authorities of the two states agree on exceptions in the worker’s interest. These agreements are discretionary — they are requested, not claimed.
Multi-state workers: a different regime, a different authority
An employee who habitually works in several member states (article 13 of Regulation 883/2004, defined at article 14(5) of Regulation 987/2009) is not a posted worker. The applicable legislation is determined by distinct criteria — starting with whether a substantial part of the activity is performed in the state of residence.
The procedural point employers miss: under article 16 of Regulation 987/2009, it is the institution of the worker’s state of residence that determines the applicable legislation — not the employer’s state. A remote or hybrid cross-border arrangement should start there.
The binding effect — and its exact limits
This is where the A1 shows its real strength. The Court of Justice has held that a certificate issued by another member state binds the host state’s institutions and courts as long as it has not been withdrawn — even if they consider it manifestly wrong (A-Rosa Flussschiff, C-620/15). Disagreement goes through the inter-institution dialogue and conciliation procedure, not unilateral disregard — including where fraud is alleged (C-421/23).
The fraud exception is narrow. In Altun (C-359/16), the Court allowed a national court to disregard a certificate obtained or invoked fraudulently — but only after the evidence has been put to the issuing institution and it has failed to respond within a reasonable time. And the issuing institution can withdraw an inaccurate certificate on its own re-examination (C-422/22).
For employers, the practical reading is double-edged: a valid A1 is a genuinely strong shield against reclassification of the affiliation — and a fraudulent one is a genuinely useless shield.
A1 and SIPSI: cumulative, never interchangeable
The A1 handles the social security layer. The French posting formalities — SIPSI declaration, representative in France, core labour terms — form a separate layer under the Labour Code, with its own sanctions. Holding one does not excuse the other.
For the labour-law side, see our guide: Posting Workers to France.
The A1 certificate — key questions
What exactly does the A1 certificate prove?
It certifies which country’s social security legislation applies to the worker — and by extension, where contributions are due. Regulation (EC) 883/2004 rests on a single-legislation principle (article 11): one worker, one applicable scheme at a time. The A1 is the portable document that evidences that determination for postings (article 12) and multi-state work (article 13). It says nothing about labour-law compliance, which is a separate framework with its own formalities.
Can the French authorities simply disregard an A1 they consider wrong?
No. The Court of Justice held in A-Rosa Flussschiff (C-620/15) that a certificate issued by another member state binds the host state’s institutions and courts as long as it has not been withdrawn — even where they consider it manifestly inaccurate. The remedy is the structured dialogue and conciliation procedure between institutions, not unilateral disregard: the Court confirmed in case C-421/23 that a host state alleging fraud must go through that procedure.
Is there any exception to that binding effect?
Fraud. In Altun (C-359/16), the Court accepted that a national court may disregard a certificate obtained or invoked fraudulently — where evidence of fraud has been put to the issuing institution and it has failed to address it within a reasonable time. Fraud is a narrow gate, not a general escape valve: an erroneous certificate remains binding until withdrawn, and the issuing institution can itself withdraw an inaccurate certificate on re-examination (C-422/22).
What about employees who work in several countries, not just one posting?
That is multi-state activity, a distinct regime under article 13 of Regulation 883/2004 (defined at article 14(5) of Regulation 987/2009). The worker is still affiliated to a single scheme, but the determination follows different criteria — starting with whether a substantial part of the activity is performed in the state of residence. Procedurally, it is the institution of the worker’s state of residence that determines the applicable legislation (article 16 of Regulation 987/2009), not the employer’s state.
What happens if no A1 was obtained before the work in France began?
Without a certificate evidencing home-state affiliation, the default territorial rule applies and French contributions can be claimed for the work performed in France — an exposure that often exceeds the labour-law fines attached to the posting formalities. The certificate should be requested before departure. Note that the A1 and the SIPSI posting declaration are cumulative obligations from different frameworks: one never substitutes for the other.
Cross-border employment questions?
We advise foreign employers on postings, multi-state arrangements and social security coordination — with the French labour-law layer handled in the same file.