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Public sector unions had a very bad day at the Supreme Court.

As the New Republic’s Elizabeth Bruenig explained in greater detail, public sector unions face an existential threat from a case that was heard before the Court today. The central question is whether the “agency fees” public-sector workers are required to pay their unions, regardless of whether they are union members or not, constitute a violation of their free speech rights, since those dues could arguably be used to promote a political agenda.

The unions in the case, Friedrichs v. California Teachers Association, have argued that the fees are necessary to do the normal business of unions, including collective bargaining. But the conservative-leaning justices appeared to agree that even that was too much. Justice Antonin Scalia summed up the prevailing view: “The problem is that everything that is bargained for with the government is within the political sphere.”

If unions are unable to collect such fees, their enterprise could prove to be financially unviable, since unions are required to represent all workers in a bargaining unit. As Bruenig writes, “At that point, it would be reasonable for union members to leave their unions and keep their dues and representation, which would collapse unions under the weight of so many free riders.”