I'm a supervisor (which is the same as shift manager at my work). My boss is the general manager so he oversees everyone and makes the schedule.
People switch shifts or pick up shifts all the time, it's very normal for scheduling conflicts or for extra hours, whatever it may be. But the last few weeks my boss has been up his ass about my girlfriend picking up shifts, specifically mine. I figured he was just being petty, but he flat out told her today she's not allowed to pick up shifts if they're mine.
Before you call me out for favoritism or PDA or anything like that, we've made it a point that work and relationship are separate. I don't treat her any different than anyone else at work. She works harder than a lot of other employees too and is constantly singled out.
She told me she's putting in her notice soon, and I'm glad. My boss is the type to have his pets that can do no wrong and complain about every little thing all the time, but the actually good workers he pushes harder and harder and complains we're not pulling our weight. I'm sick of it.