Legal help

Like others said, it would mostly depend on the laws in your state, and then also the boss to a degree. Most of the time, if this was an honest slip-up, and your brother is a reliable person who doesn't lie or do other suspicious stuff, most people would just let it slide.

Also, is there a schedule of when they're supposed to work? If your brother knows a lot of people, maybe they can talk to the boss and prove that he was working at his scheduled time (again, if your brother is known to be lazy and miss work, then it'll be harder for the boss to accept).

Beyond this, I'm not sure what else to tell you, other than consult a lawyer (but that's an expensive alternate).

Jam it back in, in the dark.