Guy's, don't get angry, get even. Bite your lip. Say nothing. Keep it at an individual level and never EVER admit to the current campaign having ANYTHING to do with your refusal to do overtime. All it takes is a few words - like you are "sympathetic" with the campaign and you are nailed.
Simply say that you would love to do OT but circumstances/ family commitments/ etc etc. stop you right now. Ask them to call you next week.
Do not EVER admit to being part of a campaign even in the tinsiest way or they will get you.
Good luck.