Comment by nickpsecurity

I'll also note that small, claims court might be able to handle a case over just a few weeks pay. He wouldn't need a lawyer for that. The risk and costs of losing are more manageable. He could send some emails about the pay he lost asking nicely citing the work he did while there. Then firmly. Then, once at a better employer, he can take the case to small, claims court.

I'd actually rather people sue over this to establish some kind of case law where companies' legal teams tell their management to make a default policy of giving the missed pay on demand. There might already be case law on it.