"Right to work" laws, existing in 24 states, mean that employees do not have to join a labor union. I support RTW laws, as the voluntary nature of the employee-union relationship requires that the union actually represent the employee or risk losing that employee's dues money.
I detest so-called "fair share" laws, like those in California, that require a union to represent me and hence require me to pay a union as a condition of employment. One might think there's a "freedom of association" issue there, but under current law there isn't. It's despicable.
Here's an extremely short exposition on labor and right-to-work history.
Aside: California teachers, if CTA/CFT doesn't represent your beliefs, check out the web site of the California Teachers Empowerment Network. (Full disclosure: I'm on the Board of Directors.)