(Reuters) – The U.S. Supreme Court on Monday turned down four cases inviting the justices to expand a 2018 ruling barring public-sector unions from collecting fees from nonmembers to also prohibit state laws requiring that a single union represent all of the workers in a bargaining unit.

The court denied certiorari in three cases involving public school teachers in Illinois and a fourth lawsuit from a New Mexico state worker. The plaintiffs in these cases also claimed they should be reimbursed for dues they paid after the high court’s 2018 decision in Janus v. AFSCME but before they formally resigned from their unions.

The Supreme Court in Janus said so-called “agency fees” that unions had collected from nonmembers for decades to fund collective bargaining violated workers’ free-speech rights.

Every federal appeals court to consider the issue, including the 7th and 10th Circuits in Monday’s cases, has rejected claims that the reasoning behind Janus also means states cannot require that a single union exclusively represent a bargaining unit regardless of workers’ membership status in the union.

Many of the cases also claim that unions’ refusal to allow members to resign immediately after the Janus ruling was issued was unconstitutional. But federal courts have upheld provisions of collective bargaining agreements that only allow union members to resign during a brief annual period.

The plaintiffs in Monday’s cases are represented by the National Right to Work Defense Foundation (NRTW), the Liberty Justice Center and Mitchell Law.

NRTW Vice President Patrick Semmens said the Supreme Court will have other opportunities this term to review exclusive union representation.

“Eventually the high court will need to step in to prevent Janus from being undermined,” he said.

The unions were represented by lawyers from Altshuler Berzon and Bredhoff & Kaiser, who did not immediately respond to requests for comment.

The Supreme Court in January declined to take up six separate cases claiming Janus applied retroactively and unions must reimburse nonmembers for previously collected agency fees.

The cases are Ocol v. Chicago Teachers Union, Troesch v. Chicago Teachers Union, Hendrickson v. AFSCME Council 18, and Bennett v. AFSCME Council 31, U.S. Supreme Court, Nos. 20-1574, 20-1786, 20-1606 and 20-1603.

For Ocol: Jonathan Mitchell of Mitchell Law

For Troesch: William Messenger of the National Right to Work Legal Defense Foundation

For Bennett: Jeffrey Schwab of Liberty Justice Center

For Hendrickson: Brian Kelsey of Liberty Justice Center

For AFSCME: Jacob Karabell of Bredhoff & Kaiser; Scott Kronland of Altshuler Berzon

For the Chicago Teachers Union: Joshua Shiffrin of Bredhoff & Kaiser

For Illinois: Jane Notz of the Illinois Attorney General’s Office

For New Mexico: Alfred Park of Park & Associates

Read more:

SCOTUS won’t decide whether Janus ruling applies retroactively

10th Circuit is latest court to swat down post-Janus challenge to public worker unions

IN BRIEF: Janus did not nix union members’ obligation to pay dues: 7th Circuit