Right-to-work laws allow workers to opt out of paying union dues while still benefitting from collective bargaining agreements — a practice that weakens unions' negotiating power. Such laws are enforced in nearly half the states, mostly in the South or in the western part of the U.S., where workers have a diminished voice on the job and face more dangers at their work sites.

This creates a "free rider" problem. Workers benefit from the protection of a collective bargaining agreement without contributing to the union responsible for negotiating their contracts, which include higher wages than most nonunion employers offer. That gives unions fewer resources to effectively enforce contracts to support workers.

It gets worse: studies show that right-to-work laws drive down wages for all workers by an average of $1,500 a year, whether they are in a union or not.