Is this legal? Forcing waiters to dishwash?

So I work for a chain resturaunt (like Olive Garden or Applebees) and the managers are always looking for ways to save money, so they cut out dishwashers on monday and tuesday nights, as well as every day from 11-5. instead, they make waiters and waitresses wash them, but they still only make minimum wage for servers (2.80 i think). Is this legal, or is there a certain amount of work they can work for that rate?