My son got a new job as a waiter.They told him that there is 2 says of training with out pay,can they do this?

He worked 7 hrs today, they didn't even clock him in or anything and they said they would get him in the computer tomorrow, but he still has to go one more day with out pay. He did not sign any papers saying they could do that. they only thing he sign was w-4 saying he was going to work there now. so can that? or do they owe him money?