That's not the way to go, at a time when the other side is clamoring for a ridiculous minimum wage. If public employee unions weren't allowed to support candidates, with either money or endorsements, they'd stop owning politicians. The unions would be fine if they only did the negotiating and provided legal protection for their members.
You are spot on. A law prohibiting political contributions by unions and a right to work law making membership non compulsory is all that is needed.