Just found out we will be working mandatory overtime the Saturday's that aren't change over weekend. So I'll be working the day of my baby shower, and invites were already made and sent out.
I would just prove you have previous plans that were scheduled before this mandatory overtime became known.
I would bring in an invite and show your supervisor. Worst case, I would take a sick day / vacation day. You definitely don't want to have to send out "notice of change" cards to each guest
My supervisor knows, I invited her. I don't have anymore vacation days or anything for the rest of the year. Only my maternity leave and we don't have sick days