Conservative nonprofits are aiming for a Supreme Court ruling to curb public-sector unions’ power by allowing them to limit the benefits they provide to workers who are card-carrying, dues-paying members, freezing out nonmembers.

Unions often call those nonmembers “freeloaders,” but that doesn’t mean they want to give up the right to represent them. “Exclusive representation” — a union‘s status as the only entity that can deal with management on behalf of workers — is a key tool of unions for getting and retaining members.