Customs audit at your company: which documents should be at hand when you use external staff

An audit by the Financial Control of Undeclared Work (Finanzkontrolle Schwarzarbeit, FKS) can rarely be planned. When customs officers stand at the factory gate, what counts is what is immediately at hand. For companies using external staff, the customs audit is a particular test. It is then not only about your own workforce, but also about workers from staff leasing, contracts for work (Werkvertrag) or subcontracting. The inspectors want to understand who is working on the premises, for whom and on what contractual basis. This article shows which documents should be in order when you use external staff, who supplies them and how you clearly assign responsibilities in your company. It does not replace legal advice; it structures shop-floor practice.

The framework has recently changed. The German act to modernize and digitalize the fight against undeclared work was promulgated in the Federal Law Gazette at the end of December 2025. Its core has applied since December 30, 2025, and individual provisions have taken effect since June 29, 2026. The audit powers of the FKS were thereby expanded and more strongly digitalized. Employers must provide documents electronically on request as well. Customs can additionally demand access to systems such as time recording. On top of that come automated data analyses, which the authority uses to select audits in a more targeted way. In practice this means that paper folders alone are often no longer enough; digital records should also be findable and readable. Which individual obligations apply to your sector depends on your situation. The legal assessment in the individual case remains with your company.

Four groups of documents are at the center. First comes the contract that underpins the assignment: the leasing agreement under temporary staffing (German AÜG, Arbeitnehmerüberlassung), a contract for work or a subcontracting agreement with a clear scope. In staff leasing, the contract also records that the lender holds the required license. Second, deployment plans showing who works where and when. Third, time records with the start, end and duration of work. Fourth, proof of identity and, where necessary, of the right to work for every person deployed. For workers posted from another EU state, the A1 certificate on social insurance is added. In some sectors, workers must also carry identity documents while working. These documentation duties for external contractors are spread across several shoulders, and that is exactly where the difficulty lies.

A customs audit of external staff therefore means one thing above all: clarifying responsibilities. The documents on the workers are supplied by whoever is their employer. In staff leasing, that is a licensed partner company that carries the employer obligations; your company remains the client site with the duties at the place of work. Under a contract for work and in subcontracting, the contractor supplies them. Your company keeps the documents on file, reviews them itself and requests missing items. That is sensible, because customs audits on site, and not every partner can be reached at that moment. A register per partner has proven itself: contract, staff list, deployment plan, hours, proof of social insurance. Name a responsible person and a deputy who know where everything is. Set a deadline by which partners must report new workers before they enter the premises.

In contracts for work, inspectors look particularly at the line between a genuine and a sham contract for work (Scheinwerkvertrag). What matters is how the assignment is actually carried out, not only what the contract says. Does your foreman give direct instructions to the contractor's workers? Do they work mixed into your shifts, according to your plan and under your supervision? Is billing by the hour rather than by result? Then a contract for work can in practice be classified as disguised labor leasing. In a genuine contract for work, the contractor organizes itself, leads its own team and owes an agreed result. The three characteristics that separate a contract for work from temporary staffing are described on our page on contracts for work. We design every model so that it is clearly separated, and we turn down anything we cannot separate cleanly.

Arbeitina acts as intermediary and coordinator. Arbeitina is neither the lender nor the employer of the workers. We handle the contract and document coordination between the partner company and the client site. In concrete terms, we bring documents together, keep an eye on handovers and follow up when something is missing. Before we place a subcontractor, it has to submit documents to us, including trade and tax registration as well as A1 certificates where required. We place selected subcontractors with complete contract documentation; more on this is on our page on subcontracting. Responsibility for the workers' documents remains with the respective employer. Whether an assignment holds up legally is assessed by your company itself as the client site.

How does an FKS audit at your company work? The inspectors usually report at the gatehouse or to plant management. They can question employees present, inspect documents and compare both with what they find on site. It helps if the named person can be reached quickly and knows where the register and the digital access points are. Inform partner companies and subcontractors immediately so that missing proof arrives promptly. Note which documents customs inspected or took with them. Order and cooperation do not turn an audit into a formality, but they make the day more predictable for everyone involved.

How can Arbeitina support your company in advance? If you use or plan to use external staff, we clarify before the first working day which documents each partner supplies and how the handover to your company works. That way every side knows who is responsible for what. No one can seriously guarantee the outcome of an official audit, and neither can we. Further answers on contract models are on our FAQ page. Describe the assignment, the number of workers and the period on our contact page. You will receive an honest assessment of which model fits and how the documents for a customs audit of external staff come together in an orderly way.