In my union good workers get paid above scale or they get promoted or they move to a different company that will pay them above scale. Also, people have reputations and if you're a complete fuckup of an employee, you will either be fired or laid off and eventually you'll find yourself on the "available for work" list down at the hall, but never getting hired because nobody wants to put up with your bullshit. You will say that it's a kind of informal blacklisting, which is true, but I'm in the union too and they can't make me hire people I know I don't want.