The United States Supreme Court has taken up a case that most legal pundits predict will deal a severe blow to government employee unions.

The court announced on Sept. 28 that it will hear the case Janus v. American Federation of State, County and Municipal Employees, Council 31 during its next term. Observers expect the court to deliver its opinion in June 2018.

Mark Janus is a state of Illinois employee who is forced to pay agency fees to his union — AFSCME Council 31 — against his will. He says that forcing public sector employees to pay an agency fee violates their First Amendment rights. Public sector unions are inherently political entities, the argument goes, so requiring government employees to make payments to a union as a condition of employment also makes an employee fund political speech.

If the Supreme Court rules in favor of Janus, as is expected, it would have the same effect as establishing a right-to-work law for public sector employees across the nation. Currently, 28 states have such a law.

Michigan passed right-to-work legislation in 2012, but Janus would still have some impact on public sector workers here.

Police and firefighters are not covered by Michigan’s right-to-work law. Also, a handful of municipalities, acting with their unions, extended collective bargaining agreements by up to 10 years or even longer just before the law took effect. This had the result of requiring employees to continue to financially support their local union despite the new law.

If the high court sides with Janus, the largest impact will be in states that don’t have a right-to-work law.

For example, the California Teachers Association collected $172 million in union dues and fees in 2016, according to a report the union filed with the federal government. That union has 325,000 members.

If right-to-work became the law in California and had the same impact on union membership there as it did on the Michigan Education Association, the California union would, within four years, lose about 72,500 members.

“With the Supreme Court agreeing to hear the Janus case, we are now one step closer to freeing over 5 million public sector teachers, police officers, firefighters, and other employees from the injustice of being forced to subsidize a union as a condition of working for their own government,” said National Right to Work Legal Defense Foundation President Mark Mix, in a press release.

The public sector unions say the Janus case is an attack on working people.

The nation’s four-largest public sector unions — the American Federation of Teachers, the National Education Association, the Service Employees International Union, plus AFSCME — issued a statement in response to the Supreme Court’s announcement:

“The Janus case is a blatantly political and well-funded plot to use the highest court in the land to further rig the economic rules against everyday working people.” It continued, “The billionaire CEOs and corporate interests behind this case, and the politicians who do their bidding, have teamed up to deliver yet another attack on working people by striking at the freedom to come together in strong unions. The forces behind this case know that by joining together in strong unions, working people are able to win the power and voice they need to level the economic and political playing field. However, the people behind this case simply do not believe that working people deserve the same freedoms they have: to negotiate a fair return on their work.”

Janus is very similar to the case Friedrichs v. California Teachers Association. The Supreme Court deadlocked on that case after Justice Antonin Scalia died in February 2016, shortly after it heard oral arguments.

The Mackinac Center for Public Policy, which publishes Michigan Capitol Confidential, has filed an amicus brief in the case, supporting Janus.