Don't let the man tell you when to work. March into there and tell them
"I'm an individual and I don't need you telling me when I need to work or not, if I want to work on Thursday I will if I don't I won't. I make my schedule not you. Got a problem with that? Find someone else to do this shitty ass job that you under pay me for. Speaking of which I deserve a 50k per year raise. Can't give me that? Then good luck with the next sucker who comes in here to conform to your fascist ways"
Go say that word for word to your boss please.