Gov. Bruce Rauner now has the Trump administration on his side in a U.S. Supreme Court case that will decide whether non-union state employees must pay “fair share” fees to cover bargaining costs.

The administration on Wednesday asked the Supreme Court to overrule a 40-year-old precedent that allows public employees to pay some fees to unions that represent them, according to a brief filed Wednesday on behalf of the administration from the solicitor general.

The court has questioned the practice twice in the past five years.

According to the brief, the case will decide whether to overrule a 1977 decision that would hold that “public employers may not compel their employees to pay agency fees to unions.” In Abood v. Detroit Board of Education, public school teachers brought a First Amendment challenge to mandatory agency fees authorized by Michigan law.

“As the nation’s largest public employer, the United States has a substantial interest in the resolution of that question,” the brief says.

Arguing that compelling public employees to subsidize their union’s bargaining position is to “force him to support private political and ideological viewpoints with which he may strongly disagree.”

The Supreme Court in late September announced it would hear the Illinois case first filed by Rauner. The plaintiff is now Mark Janus, a child-support specialist with the Illinois Department of Healthcare Services who has argued that paying union fees violates his First Amendment rights. The defendant is the American Federation of State, Council and Municipal Employees Council 31 — which has been at war with the governor since he took office in 2015.

“No person should be forced to give up a portion of their pay each month to fund public sector union activity against their will,” Rauner said in a statement in September after the Supreme Court agreed to hear the case. “It’s a fundamental violation of their First Amendment right to free speech and association. I am hopeful the court will see it that way in the end.”

Asked to comment on the Trump administration support, the governor’s office Thursday said the Supreme Court agreed to take the case “because there is a significant First Amendment right at stake which Governor Rauner has fought to protect.”

The governor began his term with an executive order that directed state agencies to comply with the First Amendment.

“The governor supports the freedom for all government workers to choose what political speech to support and whether or not to take money out of their paychecks to pay dues to a union,” Rauner spokeswoman Patty Schuh said.

The union on Thursday called the Trump administration support a “political attack,” while linking Trump and Rauner.

“This case is a purely political attack on the freedom of working people to join together and speak up for themselves and their communities,” AFSCME Council 31 spokesman Anders Lindall said. “Of course Donald Trump and Bruce Rauner are standing together against working people. They’re two anti-worker billionaire peas in a pod.”

Democratic gubernatorial candidate J.B. Pritzker on Thursday also criticized the Trump administration’s brief.

“After failed attempts to force his special interest agenda on Illinois, Rauner is partnering with Trump to roll back workers’ rights on a national scale,” Pritzker said in a statement. “This case could threaten the mere existence of public sector unions, and there is too much at state for working families to have their governor and president working against them.”