A “right-to-work” law is a statute in the United States that prohibits union security agreements, or agreements between labor unions and employers, that govern the extent to which an established union can require employees’ membership, payment of union dues, or fees as a condition of employment, either before or after hiring. Right-to-work laws do not aim to provide general guarantee of employment to people seeking work, but rather are a government regulation of the contractual agreements between employers and labor unions that prevents them from excluding non-union workers,[1] or requiring employees to pay a fee to unions that have negotiated the labor contract all the employees work under.
I believe there are 25 such states in the U.S.