You're misusing rent-seeking here. Rent-seeking would be if the union were attempting to extract these dues without returning a meaningful service to the worke

You're misusing rent-seeking here. Rent-seeking would be if the union were attempting to extract these dues without returning a meaningful service to the worker--but membership needs to be obligated, systemically, for the negotiating power to be retained. This is how you get two truly corporate individuals determining compensation through negotiation. See other replies elsewhere for more details on why this works.