I am a salaried employee. My boss said I have to stay in town on the weekend that there’s an event going on that I’m not called to in case something happens and they need me. Is this allowed?

I am pretty much always on call and always expected to check my emails. I was hoping to go away for the three day weekend before MLK day for my birthday but she said I couldn’t leave town until after this rehearsal in case they needed me.