Janus v. AFSCME is an upcoming SCOTUS case with big potential repercussions on unions.

It is a case about whether public union fair-share agreements violate the First Amendment. The 1946 Taft-Hartley Act allows union security agreements under state law. Mark Janus argues that the government allows unions to charge employees for fair-share fees without their consent, which violates free speech rights. AFSCME argues that state law allows union security agreements in order to curtail free riding since unions have a legal duty to advocate for all employees.

What are the best arguments for both sides? What factors make public unions different from private unions with regard to the law and how they are permitted to operate? Why are/are not union dues considered speech? How has SCOTUS ruled in past cases relating to unions? What factors are different about Janus than precedents that might influence the decision?