I agree that people should have the right to band together in an organized way to increase negotiating power. What I have a problem with is when joining the union and paying dues becomes expected or even mandatory.
When I was in college, I worked a summer for a high-end grocery store as a part-time bagger. Nearly every day the assistant manager (the local union representative) would accost me to join the union and to pay union dues. As a part-time and temporary employee this made absolutely no sense for my situation and would only serve to modestly increase the bargaining power and coffers of the union.
In other situations paying dues to the union becomes mandatory under the legal concept of "fair share fees" where non-union members are required to pay into the bargaining costs of the union.
> If a majority of the public employees at a given site vote to be represented by a union, that union becomes the exclusive bargaining agent for the workers. In California, some 325,000 teachers in more than 1,000 school districts are represented by the California Teachers Association and, to a lesser extent, the California Federation of Teachers.
> Of those, 9 percent have not joined the union, but under California law, any union contract must cover them too, and so they are required to pay an amount that covers the costs of negotiating the contract and administering it. The idea is that they reap the bread-and-butter benefits covered by the contract — wages, leave policies, grievance procedures, etc. — so they should bear some of the cost of negotiating that contract.