A union is different from a church, club, or being a consumer some place because it is at your job and is part of how you generate income. Non-union employees

A union is different from a church, club, or being a consumer some place because it is at your job and is part of how you generate income. Non-union employees get the same pay raises union employees do, a rational actor in a non-compulsory union shop would not join the union because they don't want to pay dues. That is why joining a union is compulsory.