Can you be fired for not working overtime

Curious if you can be fired for refusing to work more then 50 hours a week? Currently husband is working 60 hours he's miserable and he's afraid he will be fired if he reduces his hours. I feel so bad for him he's so burned out. Unfortunately he can't leave the company as his niche is so small he would have to go back to working nights and half of the pay he makes. I'm just wondering if there's any laws protecting a worker from being forced to work more overtime than what is reasonable on a weekly basis.