"Yes," your employer can require you to work overtime and can fire you if you refuse, according to the Fair Labor Standards Act or FLSA (29 U.S.C. § 201 and following), the federal overtime law. The FLSA sets no limits on how many hours a day or week your employer can require you to work.

Can you get fired for refusing to work overtime?

If an employee fails to comply with a lawful and reasonable direction to work a reasonable amount of overtime, then the employee may be guilty of serious misconduct. This would mean that you could dismiss them without notice.

Can you say no to overtime?

If your contract doesn't mention overtime

You have a right to say no but if you say no without a good reason, it might damage your relationship with your boss. They might try to change the working hours in your contract.