Employees shouldn't join unions that don't exist for their benefit. And if a union doesn't benefit the workers, they should leave and start a new union.

This happened years ago in Netherland: many railway employees weren't happy with something their union (part of the largest union federation) negotiated for them, so they left and started a competing union to negotiate for them instead. Messy, embarrassing for the big union, but it solved the problem.

Not sure if the alternative union still exists or if it merged back into the large union again.