You have a voice in wages, benefits and working conditions. Management gives you what it wants to give you. Your wages, benefits, and working conditions are protected by legal contract.
Management can change wages, benefits and working conditions whenever it wants.
If you're disciplined, management has to follow steps. If you're disciplined, you have no due process rights. If you're disciplined for something you didn't do, the union will defend you. If you're disciplined for something you didn't do, you're on your own. If you do a good job and are in line for a promotion, you'll get it.