Because most employers simply wouldn't want to deal with that. They don't want to have one set of rules for one group, and one set of rules for another. And wha

Because most employers simply wouldn't want to deal with that. They don't want to have one set of rules for one group, and one set of rules for another. And what if you are a member, get the raise, and then leave the union? Do they dock your pay back to what you were before?