mandatory but we aren't being paid

I work in childcare. we have to meet accreditation standards... one of the goals was to participate in at least 2 team building events. one of the supervisors from the other centre has decided to host a games night on the 10th of March from 6-12am .. the director decided to make it mandatory. it's on a Saturday... a day I normally have off. I also have a long day on the following Sunday and its also a potluck so I'm obligated to bring something to eat. can they do that? make something mandatory on a day off and then not pay us for it?