Public employee unions in Oregon and elsewhere may face a terrible blow to membership from the U.S. Supreme Court. Oregon unions are already trying to lock people in the union, making it hard to leave and stop paying dues.

One of Oregon’s largest public employee unions, Service Employees International Union, has a provision that members can only withdraw from the union in a narrow 15-day window that opens once a year. Another of the state’s large public employee unions, American Federation of State, County and Municipal Employees, has a provision that is even narrower. It’s 10 days. And what makes those windows more complicated is that when they occur can vary from worker to worker.

Apparently the unions are eager to fight for workers, except they want to fight workers who want to leave with their own money.

The new court case driving union concern is Janus v. AFSCME. The heart of the case is the ability of unions to require government employees to subsidize a union as a condition of working for their government. Unions argue that workers benefit from union negotiations, so it’s only fair that they should pay their share for the representation.

But the plaintiff in the case argues that requiring any sort of compulsory fee for labor negotiations violates the First Amendment. Labor negotiations are a form of political activity. The debate over the cost and size of government is directly related to negotiations over wages and benefits. So why should anyone be compelled to pay for negotiations they don’t agree with?

The Supreme Court seemed about to rule against the unions in a similar case in 2015, but then Justice Antonin Scalia died. The court split 4-4. The new make-up of the court might lead to a ruling against the unions.

Unions can still be strong if the court rules against them in Janus. But they will have to convince workers to participate, rather than compelling them to pay for representation they may not want.