I am a salary employee at a large retailer. My employer just told all salary managers they must work ten hour days with an hour lunch. Is there any limit to the amount of hours they can mandate?

I am a salery employee at a large retailer. My employer just told all salery managers they must work ten hour days with an hour lunch. Is there any limit to the amount of hours they can mandate?

What country and state would this be? Assuming USA states I have worked, they can. But local laws may vary.