The U.S. Supreme Court building in Washington. (Carlos Barria/Reuters)

The Trump administration on Wednesday asked the Supreme Court to overrule a 40-year-old precedent that allows compelling public employees to pay some fees to unions that represent them, an important tool for the U.S. labor movement.

It was another dramatic reversal in a high-profile case before the high court, and at least the third time since President Trump’s inauguration that the Justice Department has renounced its past positions, some held for decades.

It puts the administration squarely on the side of conservative legal activists, who have complained for years that the requirement violates the free-speech rights of those who don’t want to join the union or pay fees to it.

The Supreme Court precedent the administration wants to overturn says that unions may charge all employees for the cost of collective bargaining, but not for the union’s political activities. About 20 states allow that practice.

The Obama administration supported the unions in previous challenges, and when the issue was last before the court in January 2016. It appeared from oral arguments that challenge would be successful, but Justice Antonin Scalia died a month later, and the court announced that it had split, 4 to 4, on the issue.

With Justice Neil M. Gorsuch taking Scalia’s place, the court announced in September it was taking a new challenge on the issue.

"The government reconsidered the question" after the new grant, says the brief filed by Solicitor General Neal J. Francisco. "The government's previous briefs gave insufficient weight to the First Amendment interest of public employees in declining to fund speech on contested matters of public policy."

The court's decision in 1977's Abood v. Detroit Board of Education "is inconsistent with prevailing First Amendment precedent and should be overruled."

It is at least the third time since the election that the Justice Department has switched its position on an issue at the Supreme Court. While different views are expected when control of the White House moves from one party to another, they can sometimes cause problems for the government lawyers who argue at the high court.

The office of the solicitor general, which represents the government at the Supreme Court, is supposed to supply the court with a consistent view of the law without undue partisan considerations.

The Trump administration already has changed its view on one case involving worker’s rights that created a rift with the National Labor Relations Board. In another, it changed the Justice Department’s long-standing position on how states may purge inactive voters from the rolls.

The Abood decision said states could allow public-employee unions to collect fees from nonmembers to cover the costs of workplace negotiations but not the union's political activities.

The unions say losing those fees would be a heavy blow because there is no incentive for workers to pay for collective-bargaining representation they could receive free.

But conservative activists — and conservative justices in recent cases — have sharply questioned whether it is possible to separate public-employee negotiations from the kind of public-policy questions — teacher salaries and classroom sizes, for instance, and the tax dollars needed to pay for them — that are raised.

The lead plaintiff in the new case is Mark Janus, a child-support specialist at the Illinois Department of Healthcare and Family Services. The case is Janus v. AFSCME Council 31.