And what would you consider a "less coercive" form?

sw: By what right does (any)union get to determine what an individual worker's labour is worth?

I could just as easily ask by what right does management get to determine what an individual worker's labour is worth.

Should workers just be left at the mercy of what their boss' are willing to pay them? We've done that before, you know. It's why the labor movement started in the first place.