A1 Certificate for Workers at Two Agencies: Avoid Double ZUS 2026

For Polish workers posted to Denmark through staffing agencies, the A1 certificate is one of the most important documents they will ever need. It confirms that a worker continues to pay social security contributions in Poland rather than in the country where they are temporarily working. But what happens when a worker is employed by two agencies at the same time? Without a properly issued A1 certificate covering both employment relationships, the risk of paying double ZUS contributions, or facing demands from Danish tax authorities at Skat.dk, becomes very real. This guide walks through the process step by step so that both workers and agency managers can navigate this situation confidently in 2026.

Why Dual Agency Employment Creates a Social Security Problem

EU Regulation 883/2004 on the coordination of social security systems establishes a clear principle: a person may only be subject to the legislation of one EU member state at a time. When a worker holds a single contract with one Polish employer and is posted abroad, the standard A1 form covers the situation neatly. Dual employment complicates things considerably. If both agencies are registered in Poland and the worker performs activities in Denmark for both simultaneously, the A1 certificate must reflect the full picture, both employers, both contracts, and the combined scope of work.

ZUS, the Polish Social Insurance Institution, is the competent authority that issues A1 certificates for workers insured in Poland. If a worker applies for an A1 certificate based only on one agency contract while actively working for a second agency, the certificate may later be challenged. Danish authorities and Arbejdstilsynet, the Danish Working Environment Authority, have become increasingly thorough in verifying posted workers' documentation. An incomplete or inaccurate A1 certificate can expose both the worker and the agency to back-payments of contributions and administrative penalties. Accurate record-keeping from the very beginning is therefore essential, a lesson explored in depth in our article on how a 50-worker agency stopped losing money on record-keeping errors in 2026.

Step 1: Check Eligibility Before Applying

Before submitting anything to ZUS, the worker and both agencies must confirm that the situation genuinely falls under the "multi-employer" provision of EU Regulation 883/2004, specifically Article 13. This article applies when a person habitually works in two or more member states. However, if both agencies post the worker exclusively to Denmark and the worker performs no meaningful activity in Poland, the situation may instead be assessed as a standard posting under Article 12. Getting this distinction right determines which legal path to follow and which ZUS form to use. When in doubt, consulting a social security specialist or the PIP labour inspectorate is strongly advisable before filing.

Step 2: Gather the Required Documents

ZUS requires documentation from both employment relationships. For each agency, the worker needs a current employment contract or assignment confirmation, proof of ongoing ZUS contributions being paid by the employer, and a statement from the agency confirming the nature and location of the work. The worker will also need a personal identification document, their PESEL number, and any previous A1 certificates if they have been posted before. Both agencies should prepare written confirmations that they are legally registered in Poland and that the worker's social insurance is being maintained throughout the posting period.

Step 3: Fill Out the Correct ZUS Form

For workers covered by Article 13 of Regulation 883/2004, the relevant application is submitted through the ZUS electronic platform PUE ZUS, accessible at www.zus.pl. The worker or their authorised representative logs into the PUE ZUS portal and selects the application for determination of applicable legislation. It is critical to list both employers accurately in the application. Omitting one agency, even unintentionally, can result in a certificate that does not cover the full scope of the worker's activities and therefore provides no protection against dual contribution demands. Both agencies should review the draft application before submission to confirm all details are correct.

Step 4: Submit and Notify the Danish Authorities

Once the application is submitted via PUE ZUS, ZUS begins the process of issuing a decision on applicable legislation. In multi-employer cross-border situations, ZUS is also obliged to notify the relevant institution in Denmark, in practice, Udbetaling Danmark, so that the Danish side can confirm agreement or raise objections. This liaison process is governed by EU Regulation 987/2009, which sets out the practical procedures for implementing Regulation 883/2004. The worker and both agencies should keep copies of all submitted documents and any correspondence with ZUS during this period. If the worker is also registered in the Danish RUT register, both agencies should ensure their registrations are current and consistent with the information provided to ZUS. For guidance on RUT obligations, see our article on RUT registration and employer change in Denmark 2026.

Step 5: Wait for the Result and Keep Records

ZUS does not issue an A1 certificate immediately in multi-employer cases. The institution first issues a provisional decision on applicable legislation, and the Danish authorities have a period in which to respond. Only after this inter-institutional dialogue is completed does ZUS issue the final A1 certificate. During the waiting period, the worker should continue working under both contracts and both agencies should continue paying ZUS contributions as normal. Stopping contributions prematurely on the assumption that Danish contributions will take over is a common and costly mistake.

Once the A1 certificate is issued, both agencies must receive a copy and the worker must carry it, or have it readily accessible, while working in Denmark. Arbejdstilsynet inspectors are entitled to request it during site checks. On construction sites in particular, documentation checks are routine, and being unable to present a valid A1 certificate can trigger an immediate investigation. The risks of inadequate documentation on Danish worksites extend well beyond social security, as our article on workplace accidents on Danish construction sites in 2026 illustrates.

Common Mistakes to Avoid

One of the most frequent errors is applying for two separate A1 certificates, one per agency, rather than a single certificate covering both employment relationships. This approach is incorrect and will not protect the worker from dual contribution liability. Another common mistake is failing to update ZUS when one of the agency contracts ends or when the scope of work changes significantly. The A1 certificate reflects the circumstances at the time of application; if those circumstances change, the certificate must be reviewed and potentially reissued.

Workers sometimes also assume that because one agency has already handled their A1 paperwork in the past, the second agency's contract is automatically covered. This is never the case. Each new employment relationship must be assessed, and in dual-employer situations the entire picture must be presented to ZUS afresh.

Practical Advice for Agencies and Workers

The most effective approach is to address the A1 certificate question before the worker begins activities in Denmark under the second contract, not after. Both agencies should communicate openly with each other and with the worker about the documentation requirements, rather than each assuming the other has taken care of it. Maintaining a shared record of submitted applications, ZUS correspondence, and issued certificates reduces the risk of gaps or duplications. For workers, the key takeaway is straightforward: a single, correctly issued A1 certificate covering both employers is the only document that will protect you from being asked to pay social security contributions in Denmark. Apply early, apply accurately, and keep every piece of paperwork. The EU social security coordination framework is designed to help workers in exactly this situation, but only if the process is followed correctly from the start.