See current situation where the Carpenters' Union in California is pushing hard against an initiative that would make it much easier to build more housing in the state because it would also reduce requirements for union labor.
Unions are very much an in-group vs out-group phenomenon (and in many cases, the benefits are specifically to the more senior union members vis a vis the less senior ones.)
Unions are very much an in-group vs out-group phenomenon (and in many cases, the benefits are specifically to the more senior union members vis a vis the less senior ones.)