I work Sunday-Thursday day sort at a hub as an unloader. The last few months, every Sunday my full-time supervisor says he needs me to go unload the metro package trucks, instead of the usual full length trailers I unload every day. At first I did it willingly, then realized it’s unpleasant because the belt stops frequently, which I can’t control, and I’m alone all day doing it. So then I said I really don’t want to, and he said ok I’ll find someone else. After a month or so, he started asking me to do it again. When I say no he guilts me into it saying he really needs me to. Can I just be stern and say no? He is my full time supervisor and boss. I don’t know if he is allowed to make me do this when it’s not my job or what I’m on the staff sheet assigned to do.