Is it abusive if you willingly sign up for it? Doctors are on-call for emergencies. We compensate for this so I'm not clear on why its abusive if employees willingly sign up. If you don't want to be on-call, find another job.

I think if you are compensated for it, and allowed to recuperate from middle-of-the-night working, it's ok. If the employee knew this was part of the job though, and not something that was thrust upon them after they were hired.