The nation’s highest court is considering a case that could weaken public unions’ dues collection efforts and ultimately limit their power.

Mark Janus, an Illinois child support specialist, is suing the American Federation of State County and Municipal Employees over agency fees collected by the union. Illinois is among 24 states that allow unions to charge such fees even when workers don’t want a union membership.

In a hearing in late February, Janus’ attorney argued that those fees violate free-speech rights because he often disagrees with union action. AFSCME and other unions argue that Janus and other non-members still bene t from collective bargaining negotiations, a stance supported by the Supreme Court since 1977.

Across the country, workers represented by unions that depend on fair-share fees are apprehensive about how the case will shake out. Nursing home workers are frequently unionized, including some 5,000 at 53 Chicago-area facilities alone.

In California in February, nurses protested outside San Mateo Medical Center with signs that read “Patient safety comes from union strength.” Nurses also demonstrated at six other hospitals around the state to advocate for preservation of the current union rule.

A similar case brought on behalf of a teacher in 2016 ended in a tie after the death of Justice Antonin Scalia. A ruling is expected in June.