Ad Set Up

So every other sunday im scheduled to work they schedule me in the mornings but then they always ask me to come in for ad set up. Now I hate getting up that early and cutting my Saturdays short, so I usually tell them no cuz i mean if they need me they should have scheduled me and usually I have already made plans for Saturday. So my question is can always saying no get me in trouble or cause me to have a bad review? Anyone know?
My availabiltiy is open but they never schedule me for it they ask me the day before when I've already made plans. This happens every other week when I work, they won't schedule me and then ask me later on during the day if i would come in.
I would just tell them you have plans and it is on such short notice that it won't work for you. Also tell them that you'd really like to work Ad and it would be easier for you if it was on your schedule so that you can plan your outside activities better.