It's funny, when I started at Eagle the union used to tell us to tell them, show me where in the contract I'm obligated to do that? When they couldn't it became, well if I'm not obligated then it's just a request, and I'm not agreeing to the request.
If they pointed to some section that was uber vague and they were taking liberties, we were told to remind them they aren't your supervisor, and to request to be connected to a chief pilot who would make the call. Always remain polite.
Somehow, somewhere it became fly it and grieve it.... never ever understood that. If the CBA was clear, then you weren't obligated. seemed pretty simple. The unclear ones, the Chief Pilot would tell you to do it and then you'd fly it and grieve it. Scheduling was/is not a supervisor.... (at least they used to not be)