This is now being challenged for public sector workers with what seems to me to be the screwy argument that since negotiations on behalf of such workers are inevitably political, to force workers to pay for the benefits they receive from the negotiations can considered the same as forcing them to pay for "political speech" with which they may disagree, contrary to the First Amendment.
If I am getting something wrong here, I know I can count on being corrected.
My question is this: Would it now be tactically appropriate for unions to violate worker solidarity and instead insist that nonunion workers be paid less than union members? It might be hard for employers to suddenly take the negotiating stance that they want to pay people more for their work than the union was asking for. It would also clarify the benefits of union membership to those who imagine that they are somehow better off availing themselves of a free ride.