WASHINGTON — Conservative groups are wasting little time in trying to deal a crippling blow to labor unions now that Justice Neil Gorsuch has joined the Supreme Court.

A First Amendment clash over public sector unions left the justices deadlocked last year after the death of Justice Antonin Scalia. But union opponents have quickly steered a new case through federal courts in Illinois and they plan to appeal it to the high court today.

The groups say unions representing government employees violate the free speech rights of workers by collecting money from people who don’t want to join.

If the high court agrees, it could threaten the financial viability of unions and reduce the clout of labor, one of the biggest contributors to Democratic political campaigns.

The Supreme Court seemed all but certain to rule against the unions in a similar case argued before Scalia died. That case, involving a California teachers’ union, was the first of several to split 4-4 while the court was short-handed. The deadlock left in place a four-decade-old practice that lets public-sector unions collect fees from non-members to cover the costs of collective bargaining.

The Supreme Court won’t consider taking up the case until September at the earliest.

The latest appeal comes as union membership in the U.S. hit new lows last year, sinking to just 10.7 percent of the workforce. As private union membership has steadily declined, about half of all union members now work for federal, state and local government.

Most of them are in states like Illinois, New York, and California that are largely Democratic and seen as friendly toward unions.