Members of the Service Employees International Union hold a rally in support of the American Federation of State County and Municipal Employees union at the Richard J. Daley Center plaza in Chicago on Monday as the U.S. Supreme Court was hearing arguments in Janus v. AFSCME, a lawsuit that challenges unions' authority under state law to collect compulsory fees from all employees they serve. (Scott Olson/Getty Images)

Conservative and liberal justices on Monday appeared to have hardened their views since the last time the Supreme Court considered a case that public-employee unions say poses an existential threat to organized labor.

In an hour-long, often caustic oral argument, the justices largely echoed their stances from two years ago, when a shorthanded court split, 4 to 4, on whether it is unconstitutional to require government workers to pay a fee to unions representing them even when they choose not to join.

But the justice likely to break the tie — rookie Neil M. Gorsuch, who in his short time on the court has consistently sided with conservatives — said nothing Monday to hint at his leanings in a similar case.

What Gorsuch decides will have major implications for the future of organized labor, which has become a pillar of Democratic Party politics, and for millions of workers in the nearly half of the states that require payments from nonmembers to cover the cost of collective bargaining.

If the Supreme Court is often loath to acknowledge politics, the ideological subtext of the battle over public-employee unions was hard to ignore.

Justice Anthony M. Kennedy, normally the most moderate of the conservative justices, came out swinging.

Kennedy saw the unions as having a political agenda calling for “teacher tenure, for higher wages, for massive government, for increasing bonded indebtedness, for increasing taxes.”

“Doesn’t it blink reality to deny that that is what’s happening here?” he asked Illinois Solicitor General David L. Franklin, representing one of more than 20 states that allow fees for nonmembers.

Justice Sonia Sotomayor, from the other end of the ideological spectrum, was skeptical of arguments that the lawsuit was meant to protect workers from having to subsidize speech with which they disagree.

“You’re basically arguing, ‘Do away with unions,’ ” Sotomayor said to William L. Messenger, a lawyer for the National Right to Work Legal Defense Foundation, which was representing an Illinois social worker named Mark Janus. Janus said he objects to the monthly fee he pays to subsidize a union that often takes positions with which he disagrees.

Sotomayor also questioned the reliability of Solicitor General Noel J. Francisco, representing the United States. The last time such a case was before the Supreme Court, during the Obama administration, the solicitor general backed the unions and said the court should respect its 40-year-old precedent allowing such fees.

After President Trump was elected, the new solicitor general urged the opposite.

“By the way, how many times this term already have you flipped positions from prior administrations?” Sotomayor asked.

Three, Francisco answered.

While Gorsuch was silent, his very presence indicated how the court’s decisions can be shaped by politics. Because the Republican-controlled Senate refused to act on President Barack Obama’s nomination of Judge Merrick Garland in 2016 to fill the seat of the late Justice Antonin Scalia, Trump was able to put his own stamp on the court quickly. His choice of Gorsuch was cheered by some of the same conservative legal groups that have backed the challenges to public-employee unions.

The court’s 1977 decision in Abood v. Detroit Board of Education said states could authorize public-employee unions to charge nonmembers for the cost of collective bargaining but not for the union’s political activities.

Messenger told the court the division was unworkable, because collective bargaining in the public-employee realm inevitably was tied to public policy, such as whether higher taxes are needed to pay for higher employee salaries.

The First Amendment, he said, does not allow for a “compulsory fee for speech to influence governmental policies.”

But the liberal justices said the court has always recognized that the government, when acting as employer, may restrict speech rights relating to work.

As a practical matter, Justice Ruth Bader Ginsburg said disallowing the fees would simply drain the union of resources, hurting the workers’ position in collective bargaining.

And Justice Elena Kagan said the court has never been cavalier about overturning one of its precedents, especially one so relied upon.

Said Kagan: “Twenty-three states, the District of Columbia, Puerto Rico, all would have their statutes declared unconstitutional at once. Thousands of municipalities would have contracts invalidated. Those contracts probably cover millions, maybe up to over 10 million workers.”

She added: “When have we ever done something like that? What would be the justification for doing something like that?”

Messenger countered that only means “you have wide-scale First Amendment violations, as you said, in 23 states.” The court must overturn practices that can’t withstand constitutional scrutiny, he said, no matter how widespread.

Kennedy and Justice Samuel A. Alito Jr. were the toughest questioners for Franklin, the Illinois solicitor general, and David Frederick, representing the American Federation of State, County and Municipal Employees.

Alito has long been a critic of the Abood decision. Government may restrict what its employees say, Alito said, but it cannot force them to identify with something with which they disagree.

“When you compel somebody to speak, don’t you infringe that person’s dignity and conscience in a way that you do not when you restrict what the person says?” he asked Franklin.

The lawyer replied it was a fee that was required, “so it’s one step removed from compelled speech.”

Kennedy pressed Frederick on whether a union’s political views can really be separated from its advocacy for workers and said the worry about ending agency fees only proved that.

“If you do not prevail in this case, the unions will have less political influence; yes or no?” Kennedy asked.

“Yes, they will have less political influence,” Frederick answered.

Kennedy shot back: “Isn’t that the end of this case?”

No, Frederick said, because that is not the question.

States have the authority to set up collective bargaining systems that they think work for them, Frederick said. And someone subject to the mandatory fee does not lose his free-speech rights.

One, he can try to convince the union that his position is the correct one. And if he fails, “he still has his conscience and his speech to speak outside as a citizen to explain why that position is wrong,” Frederick said.

The case is Janus v. AFSCME.