The justices said the practice violates the First Amendment rights of nonmembers who disagree with the positions that unions take.
Check it out:

It’s interesting to ponder whether the other big Supreme Court decision that came down today might have even more profound ramifications than the Hobby Lobby decision against ObamaCare’s contraceptive mandates. Much will depend on how the precedents affect future cases. There are more cases that could be very bad for Big Labor coming up right behind this one.

As with the Hobby Lobby decision, there is much talk about how today’s Harris v. Quinn ruling is “limited” in scope, since it applies to a relatively narrow group – in this case, “partial-public employees.” The Associated Press sums up the decision: