Can they legally do this?

They can't tell him, but they can ask him. It depends also on what time of job he does. For example, nurses, at our facility they are required to stay on the clock until someone is there to relieve them. If they don't, they can get their nursing licenses taken away. But for example if he works at Office Depot and they said he has to stay..NO...but if he does work, they have to pay him overtime. Which is 1.5 hours extra.

If they are otherwise in compliance with the few payroll guidelines that do exist, then it is legal and he can be fired for refusing. Because it is not a contract, the manager's schedule is just that, the manager's. It can be modified at their discretion and the employer has very little recourse.

Interestingly, one of the quick draw suggestions here is "check your contract" and most do not realize how simple their contracts actually are. For the overwhelming majority, it is no more than something like "We would like to hire you. When can you start?" A standard response of right now or in two weeks completes the only covenant of offer and acceptance.

In the card game of business, the employees are the only players who never have any trumps. You are a good friend. Good luck to each of you.

Unless he's covered by either an employment contract or by a union contract then the employer can pretty much do whatever they wish. The only exceptions are protected groups; e.g., mnorities, people with disabilities, gender, sometimes sexual preference, weight, smoking; but, only if that is why they are harassed or discriminated against.

Yes they can fire him if he isn't willing to work the hours they need him, even with no notice if they just need him to stay over.