It's only possible at company's where the contract allows it... if there isn't a junior manning provision in the contract, the pilots can say "go to hell" and the flights get cancelled. (And then maybe staffing levels get adjusted...)

ACA/Independence didn't have junior manning. The result was that many crewmembers worked out deals to get trips covered. (Drop trip later with pay, pay premiums, DTR approval, etc). My philosophy was that I was more than happy to help out- as long as it wasn't taken for granted and I got something in return.