You could perhaps try framing it as a negotiation, i.e. "there was nothing in my original contract that indicated this would be one of my regular responsibilities, I'm happy to open negotiations with you in order to add that stipulation." Think of a salary at which you might actually consider being on-call (don't be charitable; make it double or triple or quadruple your current salary if you want). Then, increase that number by 50% and call it your starting offer. If they balk and try to talk you down, offer to go lower, but don't go below that number from the first step. Negotiations will almost certainly stall and your supervisor (who I presume is the one putting pressure on you) will then have political cover to tell their own supervisor (who I presume is putting pressure on them) "hey, I tried", and hopefully this will continue far enough up the chain until it reaches a person that is so detached that they don't really give a damn and drop it. If they do eventually end up firing you over this, then this indicates they would likely have fired you anyway and therefore you've not lost from this exchange. And on the slim chance that they accept your terms of quadrupling your salary, I guess you can retire substantially earlier. :P