The U.S. Supreme Court will again take up the question of whether making public sector workers pay fees to unions violates their First Amendment rights. Since 1977, the Supreme Court has upheld "union shops" where non-members may be assessed agency fees to recover the costs of "collective bargaining, contract administration, and grievance adjustment purposes" while allowing objectors to union membership to prevent having their dues used for political purposes. (see, Abood v Detroit Board of Education.)
Abood was challenged recently in Friedrichs v California Teachers Association, but last year he Supreme Court split 4-4. The case that could overturn Abood is called Janus v AFSCME and comes out of the 7th Circuit.