My question involves labor and employment law for the state of: South Carolina.
After seeing the schedule, a co-worker asked me at the beginning of the week if I could work her Easter shift for her. I told her that it would put me into overtime and that she would have to approve it with the manager. The manager asked me if I would be willing to trade one of my regular shifts in order to pick it up. I said no. At that point she told me that over-time would be okay.
Then, on Tuesday I was told that overtime was not okay. So I told my co-worker that I could not work for her.
When I checked the schedule as I left tonight I noticed that my next shift has been crossed out by my manager and I have been written in to work for my co-worker on Sunday. I did not agree to this. Nor did anyone even mention it to me. I make more money on Fridays than I do on Sundays. I am not willing to take a pay-cut in order to help out this particular co-worker. Do I have a case?
I was written into the schedule mid-week after the schedule had already been posted for days. I am pretty sure this is an act of Favortism from this particular manager toward my co-worker. She wants the day off and my manager is dead-set on giving it to her, whether I like it or not. Mind you, no one would ever do anything like this for me.
Do I have a case? At the very least can I refuse to work the shift for her without fear of termination?

