A U.S. Supreme Court case that could end with union members being able to opt out without penalty moved forward Monday, but New York City’s teachers union says its members won’t abandon it.

The case, Janus v. AFSCME Council 31, challenges “agency fees” that some unions, including the United Federation of Teachers, charge nonmembers who benefit from collective bargaining. The court is seen as likely to strike down those fees, potentially diminishing unions’ membership and power. Read our primer.

As Supreme Court justices heard oral arguments in the case Monday morning, the United Federation of Teachers distributed a confident statement from President Michael Mulgrew, along with pictures from four schools where teachers had amassed to back the union.

“The Janus case is bankrolled by right-wingers who want to cut salaries, dictate working conditions and roll back 50 years of hard won civil and workers’ rights,” Mulgrew said in the statement. “That’s why they going after one of the remaining institution that stands up to them – unions. But educators aren’t falling for it. We are sticking with our union.”

The four schools represented are — clockwise, starting at the top left — PS 134 in Manhattan, PS 131 in Brooklyn, PS 1 in Brooklyn, and MS 821 in Brooklyn. Teachers at the schools held signs distributed by the union and also made their own.

Today’s court arguments offered some hints about the case’s direction, according to a blog that analyzes Supreme Court news. The court’s four liberal justices appeared to be taking a wide lens when considering the legality of agency fees, according to SCOTUSBlog, while the newest justice, Trump appointee Neil Gorsuch, said little. He is seen as likely to cast the deciding vote on the case later this year.