Is repayment arrangement in employment contract legal?

Questioner

One of our candidates (from Serbia) is employed at COMPANY and has a two-year contract expiring in June 2023. He earns 2500 gross in his first year and in his second year he will earn 3000 gross. If he leaves the company early, he will have to pay back part of his monthly salary. If he leaves in his first year, that is 1000 euros per month that he leaves early. And when he leaves in his 2nd year, that is 500 euros per month. Is that legal? I'd like to hear from you, thanks in advance.

Lawyer

I can imagine that a subdistrict court judge would at least look very critically at such a repayment arrangement, because in this way the employer could make it very difficult to leave somewhere in the meantime, while the starting point is, and I assume this will also be stated in the employment contract, that you must be able to terminate (provided that the agreed termination provisions are observed). In any case, the arrangement must not result in this person earning less than he or she is legally and/or under a collective labor agreement.