The issue is that the union provides a public good. Strike for a pay rise? Your non-union colleagues will get that too. Hire a lawyer to sue for better health and safety? Employees who never paid their dues will benefit.

These concerns don't persuade me personally that Right to Work laws are bad. I'm just telling you they exist and probably have some validity.

I worked for UPS for a long time, and if I am understanding what you are saying then no, you must be a due-paying member of the IBT to benefit from contractually-negotiated benefits and pay. UPS corporate has a totally different set of benefits, pay, and expectations from their Teamster counterparts.

I may have misunderstood what you meant though.

Compulsory union membership strengthens collective bargaining by preventing defections. Game theory 101.

https://en.wikipedia.org/wiki/The_Logic_of_Collective_Action

The doublespeak "Right to Work" sabotages collective bargaining, disempowering Labor.