PayTjek verifies payslips and employment contracts against Danish collective agreements, with a level of certainty that probabilistic AI cannot offer. Korrekthed. Ikke sandsynlighed. Correctness, not probability. The problem Pay errors are widespread, yet very few payslips ever get checked. Collective agreements are complex, and checking payslips by hand is slow work for trained case handlers. As a result, trade unions only reach a small fraction of the payslips where errors hide, and members lose money they are owed. Our solution PayTjek is an internal tool for trade unions. We combine the latest within AI and machine learning with a deterministic rule engine: AI reads documents and extracts the rules from collective agreements, and the rule engine validates every rule and every calculation. Members upload their payslip through an app. The case handler works in a case flow where every error comes with a direct reference to the relevant clause in the collective agreement and a plain explanation, so the case handler can act right away and has the documentation ready to raise the claim. Member and union can follow up with each other directly in the flow. This lets trade unions offer payslip checks as a natural part of their membership offering, at a scale that was not possible before, without adding pressure on their resources. Our ambition We are a young company with big ambitions. We start with Danish trade unions and the Danish labour market, and our goal is to make payslip verification a standard part of what unions offer their members across Europe. PayTjek was founded in Copenhagen in 2025 by Theis Thøger Veddinge and Anton Gammelmark Andersson, with roots in research on formal verification, and is supported by Innovationsfonden.