Comment by Dayshine

> 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

In the US. In the UK all the major unions I know don't require membership and fight for all employees in the industries they represent. E.g. as a software developer on a research project at a University I got all the negotiated benefits of the academic Union.