[XplicitLuder]

usually they set up a schedule, where perhaps every second week you'll work a saturday (so itll be OT) or w/e, but i think you most likely will be told in advance. If you can't work it or you dont want too then you should ask a co-worker , as SG said, to cover your shift.

but re-reading your post again you said it was an "on-call" shift ? so meaning lets say youre off on the saturday and theyll call you the friday night before askin you to work saturday? (something like that, doesnt have to be what i just said) my gf usually got those at her work and well it was up to her if she wanted to work or not. She would tell em ya i can come in or no i cant. Let's phase it, unless you are the LAST resort, im sure they can find someone else to cover that OT day that you chose to say no too.