My boss told me one one of my days off I must come in and clean for 3hrs for free is that legal

He can ask, but he can't demand that you work for free, not unless this is an agreement you made when you first took the job.

The thing is, he doesn't need a reason to fire you. If you choose not to go in and clean, he could well decide to terminate your employment. It really depends on you. Do you want to risk losing your job, or do you want to work for 3 hours for free?

Well would I be protected under the fair labor law act. We were salaried employees. And never got paid for the hours we worked past what we were scheduled. Now they changed us to hourly. Because they want us to get paid for the hrs we work. Now they want me to do the opposite. I manage at a national fast food chain

If you are salary, you are expected to come in and work anytime they want and not get paid extra. Salary employees often work 60 to 80 hours a week.

If you are a hourly employee, they are required to allow you to clock in and pay you for the time you work.