I work in a retail store as a salaried manager. My GM often scheduels me for less than 40 haours a week. I do not ask for this time off nor does he ask me if I want to take the time off. I am forced to take PTO to make up my 40 hours, however I do not get paid overtime if I am schedueld more than 40 hours. Is this legal?

Assuming that you are correctly classified as exempt, yes, it is. It may be petty. It may be unfair. But it is legal, and it is not uncommon.