The A1 Certificate Explained: Posting Workers Across EU Borders Without Tax Trouble
If your employee crosses an EU border for work, even briefly, you need an A1 certificate. Here's when the rule bites and how to get one without delaying the trip.
An A1 certificate is a document issued by the social security authority of the worker's home country, confirming that the worker remains subject to that country's social security system while working temporarily in another EU/EEA/Switzerland member state. The certificate is the legal proof that the receiving country's social security cannot demand contributions for the duration of the posting.
The A1 sounds bureaucratic. It is bureaucratic. It is also legally required from the first day of any cross-border work assignment in the EU, and missing one has caused real fines for real companies.
When you need an A1
The certificate is required whenever an employee crosses into another EU/EEA member state or Switzerland to:
- Attend a multi-day client meeting or conference
- Service a customer site
- Travel to a sister office for project work
- Work remotely from a coworking space or hotel for more than incidental time
The threshold is not "long-term posting" — it is any work activity that crosses the border. Even a one-day workshop in Berlin for a Spanish-employed consultant technically requires an A1, and enforcement officers in Belgium, France, Germany, and Austria have ramped up spot-checks at conference centres and client sites since 2023.
How to get one
The process is country-specific but follows a common pattern. The employer applies to the home country's social security authority — INPS in Italy, URSSAF/CLEISS in France, DRV in Germany, ZUS in Poland — typically through an online portal, sometimes with weeks of lead time. The portal at the European Commission's posting of workers page lists the competent authority in each member state.
For frequent travellers, employers can request a multi-state A1 valid for up to 24 months. Single-trip A1s are usually issued retroactively if forgotten — but if a labour inspector requests one during the trip, retroactive issuance does not protect against the fine.
How this interacts with the rest of your mobility stack
The A1 is one of three documents that travel with a posted worker:
- The A1 certificate for social security continuity
- A prior notification to the host country's labour inspectorate (required in most western European countries under the Posted Workers Directive)
- The employment contract or assignment letter documenting the assignment terms
If you are working with independent contractors instead, A1 is not the right document — they need their own social security certificate as a self-employed person. And if your team is expanding into a country fast enough that A1 churn is getting unmanageable, an Employer of Record arrangement starts to make sense; see our comparison of Deel for the EOR market.
HourSquare's onboarding module includes A1 application templates for the most common posting countries, and the A1 glossary entry has worked examples by country.