By Adam Liptak

New York Times News Service

CHESTER, Ill. — Randy Clover is something of an anomaly — the president of a union local that represents Illinois state employees and a Republican precinct leader who voted for President Donald Trump. But he has no doubt about what will be at stake next week at the Supreme Court: the financial and political clout of one of organized labor’s last strongholds.

The court will hear arguments Monday about whether the government employees represented by Clover’s union, the American Federation of State, County and Municipal Employees, must pay the union a fee for representing them in collective bargaining. Conservative groups, supported by the Trump administration, say the First Amendment bars forcing government workers from having to pay anything, and the court has sent strong signals that it agrees with that argument.

If it does, unions like Clover’s stand to lose fees not only from workers who object to the positions they take in negotiations but also from anyone who chooses not to join a union but benefits from its efforts. To hear Clover tell it, the case is the culmination of a decades-long assault against the labor movement.

“The case was started by the governor to destroy unions,” Clover said, referring to Gov. Bruce Rauner, a Republican who has been at war with Illinois’ public-sector unions.

A ruling against public unions is unlikely to have a direct impact on unionized employees of private businesses because the First Amendment restricts government action and not private conduct. But unions now represent only 6.5 percent of private-sector employees, down from the upper teens in the early 1980s.

Groups financed by conservative donors have worked hard to weaken public unions, and denying them the ability to impose mandatory fees on workers has been a long-sought goal. The argument almost succeeded in 2016, when the Supreme Court seemed poised to rule that the fees were unconstitutional.

But Justice Antonin Scalia died not long after the earlier case was argued, and it ended in a 4-4 deadlock. The new case, which had been filed in 2015, was waiting in the wings and soon reached the Supreme Court. By the time the justices agreed to hear it, Rauner’s claims had been dismissed, and the case is now being pursued by Mark Janus, a child support specialist for the state of Illinois.

The Supreme Court is back to full strength with Trump’s appointment of Justice Neil Gorsuch, and most observers believe the new justice will join the court’s other conservatives to deliver a decision that will hurt public unions.

To decide against the union, the Supreme Court will have to overrule a 40-year-old precedent, Abood v. Detroit Board of Education. The decision drew a distinction between forced payments for a union’s purely political activities, which it held were forbidden by the First Amendment, and ones for more conventional union work, like bargaining, contract administration and representation of workers in grievance proceedings.