Is there a fast food union?
Anyway, yes that certainly can and does happen, but humans kind of suck man. Before unions and collective bargaining were a real, protected thing it was the companies that were holding the workers hostage. Literally... going back to Carnegie again his workers tried to unionize and strike because working conditions were abhorrent. That ended in people dying:
Homestead Strike - Wikipedia, the free encyclopedia
Unions are meant to be a check and balance for corporate greed and they work well at doing that. However, they also can and do become corrupt organizations themselves. It's not a perfect system but it's better than it was before they were around. Restructuring of unions is reasonable, abolition is not.