A Czech engineering company wins a six-month service contract with a Warsaw-based manufacturer. The project starts in three weeks. Five specialists are needed on-site in Poland. The HR manager assumes that EU freedom of movement covers everything – no formalities required. That assumption, it turns out, is expensive.

Czech employees posted to Poland remain subject to Czech social security, provided their employer holds a valid A1 certificate issued by the Czech Social Security Administration (Česká správa sociálního zabezpečení, ČSSZ) before the posting begins. Under EU coordination rules, a missing or late A1 certificate exposes the employer to double social security contributions – in both Poland and the Czech Republic – for the entire posting period. The Polish Social Insurance Institution (Zakład Ubezpieczeń Społecznych, ZUS) has authority to challenge the home-state coverage and demand Polish contributions retroactively, with no cap on the look-back period.

This case study examines a real matter we handled for a Czech technology group posting workers to Poland. We have anonymised all identifying details. The matter illustrates how a procedural gap – not a legal dispute – can generate six-figure liability within months.

What was the background of this posting matter?

Our client, a Czech IT services company, held a framework agreement with a Polish telecoms operator. Under the agreement, the client deployed rotating teams of network engineers to sites across the Mazowieckie and Silesia regions. Postings typically ran between two and five months. The client had been operating this model for approximately 18 months before contacting us.

The trigger was a ZUS inspection at the Polish operator's premises in autumn 2025. ZUS auditors requested A1 certificates for all foreign workers present on-site. The Czech company's HR team produced certificates for three engineers. Two others had no certificates at all. A sixth engineer held a certificate that had expired six weeks earlier – the posting had been extended informally, without notifying ČSSZ.

ZUS issued a preliminary assessment within 30 days of the inspection. The assessment proposed that the two uncovered engineers and the engineer with the expired certificate had been subject to Polish social security from the first day of their respective postings. The aggregate liability, including interest, exceeded PLN 180,000. The client had 14 days to respond before the assessment became binding.

  • Three engineers: valid A1 certificates – no issue.
  • Two engineers: no A1 certificates obtained at any point.
  • One engineer: A1 certificate expired mid-posting due to unnotified extension.
  • Preliminary ZUS liability: PLN 180,000 including statutory interest.

What strategy did we apply to challenge the ZUS assessment?

The strategy rested on two parallel tracks. First, we engaged ČSSZ directly to obtain retroactive A1 certificates where the factual conditions for posting were demonstrably met. Second, we filed a formal objection with ZUS challenging the assessment on procedural and substantive grounds, buying time for the ČSSZ process to run.

EU coordination law provides that a competent institution in the home state – here, ČSSZ – retains authority to issue an A1 certificate even after a posting has begun, provided the underlying conditions (genuine economic activity in the home state, temporary character of the posting, and the worker's habitual employment by the sending employer) are satisfied. The certificate, once issued, is binding on ZUS under the principle of mutual recognition. ZUS cannot unilaterally disregard a valid A1 certificate; it must initiate a dialogue procedure with ČSSZ if it disputes coverage.

For the two engineers with no certificates, we gathered evidence of their Czech employment contracts, Czech payroll records, and the client's Czech tax registrations. We submitted a retroactive application to ČSSZ within ten days of receiving the ZUS assessment. For the engineer with the expired certificate, we filed an extension notification and requested a corrected certificate covering the extended period. ČSSZ acknowledged both applications within five working days.

We secured a reversal of a ZUS preliminary assessment exceeding PLN 150,000 for this Czech technology client operating across Mazowieckie and Silesia (autumn 2025). The remaining liability – approximately PLN 30,000 relating to a period where retroactive certification was not available – was settled by agreement.

How did the process unfold step by step?

The timeline mattered. ZUS's 14-day response window is short. Missing it forfeits the right to object and converts the preliminary assessment into a final decision enforceable by bailiff within a further 30 days. We filed the objection on day 11, citing the pending ČSSZ applications as grounds for suspension of the ZUS proceedings.

ZUS has discretion to suspend enforcement pending dialogue with a home-state institution. That discretion is not automatic. We submitted a detailed legal memorandum citing the EU Social Security Coordination Regulation and the binding nature of A1 certificates under the European Court of Justice's established case law. ZUS agreed to suspend the assessment for 60 days.

ČSSZ issued the retroactive A1 certificates for the two uncovered engineers within 45 days. The certificates covered the full posting periods. We transmitted them to ZUS immediately. ZUS withdrew the portion of the assessment relating to those two engineers – PLN 152,000 of the original PLN 180,000 demand – within a further 15 days.

The residual liability of approximately PLN 28,000 related to the gap period on the extended posting, where the engineer had been working in Poland for six weeks after the original certificate expired and before any extension was filed. That gap was not curable retroactively. We negotiated a payment schedule with ZUS over three monthly instalments, avoiding enforcement proceedings entirely.

  • Day 1–11: ZUS objection filed; ČSSZ retroactive applications submitted.
  • Day 12–45: ČSSZ issues retroactive certificates; ZUS suspension in place.
  • Day 46–60: ZUS withdraws PLN 152,000 assessment; residual PLN 28,000 negotiated.
  • Total exposure eliminated: approximately 85% of original assessment.

For context on how similar coordination challenges arise when posting workers from other EU jurisdictions, see our analysis of relocating employees to Poland from the Netherlands and our parallel review of employment law compliance for Slovak companies operating in Poland.

What lessons apply to every Czech employer posting workers to Poland?

The case carries four transferable lessons. Each addresses a specific failure mode that recurs across cross-border posting arrangements, regardless of the sector or the size of the employer.

Apply before the posting starts. A1 certificates must be in place on day one. ČSSZ typically processes standard posting applications within 30 days. Build that lead time into every project timeline. A contract signed today means the A1 application should be filed today – not on the employee's first day in Warsaw.

Track extension dates actively. The single most common failure is an informal posting extension. When a project overruns, HR teams focus on the project, not the certificate. Set a calendar alert 30 days before each certificate expiry. Filing an extension with ČSSZ costs nothing. Failing to file can cost PLN 30,000 or more per worker.

Understand the work permit question separately. A1 certificates govern social security only. They do not address work permit Poland requirements, which for Czech citizens (EU nationals) are generally not required for employment. However, the regulatory picture changes if the posted worker is a third-country national employed by the Czech entity. In that scenario, separate Polish work authorisation may be required alongside the A1 certificate – a point that often surprises Czech HR teams unfamiliar with Polish immigration rules.

Prepare for ZUS inspections proactively. ZUS has increased cross-border posting inspections since 2024. Inspectors arrive at the Polish client's premises, not the Czech employer's office. The Polish host entity may face its own liability if it cannot demonstrate that posted workers hold valid social security coverage. Maintaining a real-time register of all posted workers and their A1 certificate validity dates – accessible at the Polish site – is no longer optional.

Czech employers with technology operations in Poland should also review their broader regulatory exposure. Our practice covers the intersection of posting rules and Czech technology and IP matters in the Polish market, where employment and IP compliance frequently overlap in outsourcing and software development arrangements.

What to prepare before posting Czech workers to Poland:

  • Confirmed A1 certificate from ČSSZ for each worker, valid for the full posting period.
  • Employment contracts confirming Czech law as the governing law of employment.
  • Evidence of the Czech employer's genuine economic activity in the Czech Republic.
  • Written posting notice to the Polish host entity, including start date and expected duration.
  • Internal calendar tracking certificate expiry dates and extension deadlines.

A ZUS enforcement decision, once final, precludes any retroactive challenge. The 14-day objection window is hard. Missing it forfeits the employer's right to contest liability entirely – a consequence that is genuinely irreversible.

Every Czech company posting workers to Poland faces a specific compliance window. Acting within that window determines whether liability is eliminated or locked in. To discuss how these rules apply to your posting arrangements, contact info@kordeckipartners.com.

Frequently asked questions

Q: Can a Czech employer obtain an A1 certificate retroactively after a ZUS inspection?

A: Retroactive certification is possible where the factual conditions for posting were met throughout the period in question. The Czech Social Security Administration has authority to issue certificates covering past periods, and those certificates bind ZUS under EU coordination rules. However, retroactive certification is not guaranteed and depends on the quality of evidence submitted. Employers should not rely on retroactive applications as a routine strategy – prospective compliance remains the only reliable approach.

Q: How long does it take and what does it cost to obtain an A1 certificate from ČSSZ?

A: Standard ČSSZ processing takes approximately 30 days for a straightforward posting application. There is no state fee for the application itself. The practical cost is the time required to gather supporting documentation and, where legal assistance is needed, professional fees. Delays typically arise from incomplete applications rather than ČSSZ processing backlogs. Filing a complete application on day one of the posting project avoids almost all timing risk.

Q: Does the whistleblower Poland framework affect posted workers?

A: Polish whistleblower legislation applies to entities operating in Poland above certain employment thresholds. A Czech employer posting workers to Poland does not automatically become subject to Polish whistleblower obligations solely by reason of the posting. However, where the Czech employer has a permanent establishment or a Polish subsidiary, those entities must comply with Polish whistleblower rules independently of the posting arrangement. The interaction between posting status and Polish employment law obligations is a common source of uncertainty for foreign employers entering the Polish market.

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 cross-border employment, global mobility, and posted worker compliance. 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.