Does you know if it is legal to force a salaried employee to take time off without pay?

My friend works for a training facility that is open nearly 365 days a year. So he works for a few hours almost every day. Recently business has slowed down dramatically and he has been told he will not be paid for a few weeks since there are little or no students. This has happened for almost a month. He does not recall any documentation or discussion when he was hired regarding this. Obviously he should look for a new job. But does he have any legal rights to get compensated from the company?