My work suddenly decided on Saturday that they wanted me to work on Sunday for 3hrs to get the store ready for competition opening up soon (turned down) Then told that the rota has been done for the month and that I AM working 10-4 Sunday the 23rd Dec. My store has never opened on a Sunday EVER (or at least in the 6yrs i've been there). I have said no to this but have been told that I need to talk/explain myself to the store manager. I have already made plans with my ds for that day. AIBU?