SCOTUS is considering Janus vs. AFSCME, a lawsuit that challenges public sector labor unions from collecting fair share union dues from members who decline joining bargaining groups while benefiting from the representation.

This case has not yet been set for argument. Keep updated here:
http://www.scotusblog.com/case-files/terms/ot2017/

See an article on how this will affect California Unions from the SacBee:
http://www.sacbee.com/news/politics-government/the-state-worker/article180426706.html