Your son can sue for the pay he is owed: all employees must be paid for all hours worked. You son can use testimony (including his and co-workers) to prove that he worked more hours than he is being paid for. Given the amount of money likely at stake, suing in small claims court, where you son can act as his own attorney ("pro se") probably makes sense, to reduce legal costs. If you son can prove by a "proponderance of the evidence" (that is, that it is "more likely than not") that we worked the additional hours, a court can order that he be paid for them.