Can employer fire you for not staying ot or coming in on days off. Sc

I can't post a pic of his attendance handbook but I don't see anything about overtime being mandatory or anything like that. It does say they can modify the schedule based on needs. My husband works m-f 6am to 2pm but they will make him stay til 10pm and before when he worked 5am to 5pm they would have him come in 7 days in a row have 1 day off and then work like 5 in a row again. It was supposed to be 4 on 4 off. He lives like an hour from the job so when u take that into consideration these are really long days. He says that he can't tell them no or they'll fire him. He said they tell him if he doesn't do it when they ask they'll draft him and he has to do it or he gets written up and after 3 write up they fire him. They also do not accept doctor's notes so if he's sick he gets written up. Is this legal? He won't quit because he likes it for the most part and it pays better than anything else around here.