A Luxembourg-based technology company sends three engineers to its Warsaw subsidiary for a six-month project. The engineers remain on the Luxembourg payroll. Without a valid A1 certificate, each of them is exposed to double social security contributions – paying into both the Luxembourg and Polish systems simultaneously. The financial exposure per worker can reach tens of thousands of euros before the assignment ends.

Workers posted from Luxembourg to Poland remain subject to Luxembourg social security law, provided their employer obtains an A1 certificate before the assignment begins. The certificate is issued by the Luxembourg social security authority, the Centre commun de la sécurité sociale (CCSS), and must be presented to Polish authorities on request. Assignments lasting up to 24 months are covered under the EU social security coordination rules that apply between all EU member states, including Luxembourg and Poland.

This alert explains who needs an A1 certificate, what happens when one is missing, and what steps Luxembourg employers must take before sending workers to Poland. The rules apply to employees, self-employed individuals, and seconded civil servants alike.

Who is affected and what are the thresholds?

The EU social security coordination framework covers any worker habitually employed in Luxembourg who is temporarily sent to perform work in Poland. The key threshold is duration: the posting must not exceed 24 months for the standard certificate to apply. Assignments beyond that limit require a separate bilateral agreement between the competent authorities of both states.

Three categories of workers are affected. First, employees posted by a Luxembourg employer to a Polish entity within the same corporate group. Second, self-employed persons who normally work in Luxembourg and temporarily extend their activity into Poland. Third, workers employed by temporary work agencies established in Luxembourg and placed with user undertakings in Poland.

  • Employees on standard employment contracts posted for up to 24 months
  • Self-employed persons temporarily active in Poland
  • Agency workers placed with Polish user undertakings
  • Civil servants and equivalent public-sector staff

The posting employer must continue to pay social contributions in Luxembourg throughout the assignment. The employer must also maintain a genuine and substantial activity in Luxembourg – not merely an administrative presence. Polish authorities, including the Social Insurance Institution (Zakład Ubezpieczeń Społecznych, ZUS) and the National Labour Inspectorate (Państwowa Inspekcja Pracy, PIP), are entitled to request the A1 certificate at any time during the posting.

One practical point worth flagging: a Luxembourg employer sending workers simultaneously to multiple EU countries faces a more complex analysis. If the worker performs more than 25 percent of their working time in Poland, the applicable legislation determination shifts, and a multi-state worker assessment is required rather than a standard posting certificate.

What are the consequences of missing or invalid A1 documentation?

An absent or invalid A1 certificate triggers immediate exposure to Polish social security contributions. ZUS may reclassify the worker as subject to Polish legislation from the first day of the assignment. The employer then faces retroactive contribution demands covering the entire posting period – potentially 24 months of arrears. Interest accrues from the date each contribution was due.

We secured a reversal of a retroactive ZUS contribution assessment exceeding PLN 180,000 for a logistics client whose posted workers from the Mazowieckie region were caught without valid A1 documentation during a PIP inspection in autumn 2025. The reversal required obtaining retroactive confirmation from the CCSS and presenting it within a 30-day appeal window.

Beyond social security, the absence of an A1 certificate may trigger scrutiny under Polish posted worker legislation. Poland implemented the EU Posted Workers Directive through the ustawa o delegowaniu pracowników w ramach świadczenia usług (Act on Posting of Workers in the Framework of Services Provision). Under that Act, the Polish entity receiving posted workers must notify the National Labour Inspectorate before the posting begins. Failure to notify carries a fine of up to PLN 30,000 per inspection finding. That consequence is irreversible once the inspection report is finalised.

For assignments involving workers who hold an EU Blue Card or are subject to a work permit Poland requirement – relevant where non-EU nationals are employed by the Luxembourg entity – the documentation burden is heavier still. Their right to work in Poland must be separately verified, independent of the A1 certificate.

To receive an expert assessment of your posted worker documentation, contact info@kordeckipartners.com.

What immediate steps must Luxembourg employers take?

The A1 application must be submitted to the CCSS before the posting begins. Retroactive applications are possible in limited circumstances, but Polish authorities are not obliged to accept them without challenge. The safest approach is a pre-posting application with at least 10 working days of lead time.

Our team obtained a confirmed A1 certificate for a financial services client in Lower Silesia within 12 working days of instruction, allowing a time-sensitive project deployment to proceed without interruption in spring 2026.

Employers should also prepare the following documentation package before the worker crosses the border:

  • Original or certified copy of the A1 certificate
  • Written posting agreement or assignment letter specifying duration and work location
  • Evidence of continued Luxembourg social security contributions
  • PIP notification filed with the National Labour Inspectorate in Poland
  • Proof of the employer's genuine activity in Luxembourg (payroll records, registered office documentation)

For companies with recurring cross-border assignments, a standing compliance protocol reduces per-posting risk. This is particularly relevant for employers who also post workers to other EU jurisdictions – the analysis for Switzerland, for instance, follows different rules, as explained in our guide on posted workers from Switzerland to Poland and A1 certificates. Luxembourg employers with Polish subsidiaries facing financial distress should also review our analysis of cross-border insolvency involving Poland and Luxembourg, where posted worker claims interact with insolvency proceedings. Employers operating across multiple EU jurisdictions may also find our note on employment law compliance for United Kingdom companies in Poland a useful comparative reference.

Whistleblower protection rules in Poland (relevant under the ustawa o ochronie sygnalistów, the Act on Whistleblower Protection) may also intersect with posted worker compliance. Workers who report social security irregularities to ZUS or PIP are protected from retaliation. Luxembourg employers should ensure their internal reporting channels cover this scenario. An employment lawyer Warsaw can advise on integrating whistleblower Poland obligations into a posted worker compliance framework.

For a tailored strategy on posted worker documentation and PIP notification, reach out to info@kordeckipartners.com.

Frequently asked questions

Q: Can the A1 certificate be obtained after the posting has already started?

A: Retroactive applications to the CCSS are technically possible, but Polish authorities are not required to accept them without scrutiny. ZUS may still assess Polish contributions for the period between the posting start date and the date the certificate is issued. Applying before the assignment begins – ideally at least 10 working days in advance – is the only way to avoid this gap entirely.

Q: Does the 24-month limit apply to the total time worked in Poland or to a single assignment?

A: The 24-month limit applies to a single continuous posting. If a worker is posted, returns to Luxembourg, and is then posted again, the second assignment is treated separately – provided there is a genuine interruption. However, if the interruption is artificial, authorities in both countries may aggregate the periods. There is no fixed minimum break required by regulation, but practice suggests a return to substantive Luxembourg-based work is necessary.

Q: Are there any posting rules that apply specifically to non-EU nationals employed in Luxembourg?

A: Yes. Non-EU nationals employed by a Luxembourg entity who are posted to Poland must hold a valid right to work in Poland independently of the A1 certificate. Depending on their nationality and residence status, this may require a separate work permit or a document confirming their EU long-term residence status. The A1 certificate addresses only social security legislation – it does not grant any immigration or work authorisation in Poland.

KORDECKI & Partners is a law firm based in Warsaw and Krakow, advising business clients across 30 jurisdictions. Our team combines expertise in Polish and international law with a practical approach to employment compliance, posted worker documentation, and cross-border mobility. We work with Polish entrepreneurs, foreign investors, and in-house legal teams. To discuss your situation, contact info@kordeckipartners.com.

Disclaimer: This publication is provided for informational purposes only and does not constitute legal advice. The information herein should not be relied upon as a substitute for professional legal counsel tailored to your specific circumstances. KORDECKI & Partners assumes no liability for actions taken or not taken based on the contents of this material. For advice regarding your particular situation, please contact info@kordeckipartners.com.