Pennsylvania is an at will employment state. That means if you do not have an employment contract or in a union you can be fired for whatever reason they want. Hypothetically, you can sue your employer for wrongful termination if the circumstance is truly egregious but lawyers cost money so it's not worth the time for most normal people.

So long as you're paid time and a half past 40 hours to your employer can demand you to stay for 12 hours. I've heard 16 but I'm not sure about that.