A fairly topical debate these days is whether it is morally justifiable to force individuals to join a labor union as a condition of employment. My view is an employer should not be allowed to coerce a potential employee to join a union in order to get the job. This is the same thing as forcing the employee to agree with the positions and viewpoints of the union. Finding a decent, stable job these days is tough. So it is easy to see how an employee could be coerced into joining a union in order to get the job!
The opposite side of this coin is the Norris-LaGuardia Act which made it effectively illegal for federal courts to intervene in Labor Management disputes. In particular, this act prevented the enforcement of “yellow dog” contracts. A “yellow dog” from the employer perspective is an employee who is a member of a union. So before the Norris-LaGuardia legislation passed, employees could force their workers to not be a member of a union as a condition of their employment. After the passage of this legislation, federal courts had a much harder time granting injunctions and forcing employees to not join unions.
Walter E. Block writes lucidly and incisively in Psychology Today describing a yellow dog contract as one in which a potential worker disavows being a member and promises not to join a labor union in order to secure employment.