Right-leaning legal activists along with Elon Musk’s artificial intelligence company have brought sweeping challenges against a cornerstone of legal enforcement in the United States: the right of private groups, people and local governments to sue over violations of many major laws.

Their argument, supported by the Trump administration, is that the Constitution reserves tremendous power for the president and federal agencies to decide how — or whether at all — to enforce federal law. They contend Congress should never have handed that power to others through so-called citizen suits that are part of environmental, campaign finance and certain other laws.

Environmentalists say it would be devastating to lose this essential, decades-old tool that is used to impose fines and halt lawbreaking by bad actors. Citizen suits, for example, have extracted millions from heavily polluting oil and gas operations, and ensured that lead pipes in Flint, Michigan, would be removed after its water crisis.

Legal experts say four pending federal cases — one of them filed last week — are moving forward at a time when the conservative majority on the Supreme Court gives opponents of citizen suits a greater chance than ever of success. The hard part for those opponents now is winning early federal cases and creating disagreement between the country’s appeals courts, which may help convince the Supreme Court the issue is important enough for a nationwide ruling.

Back in 2000, a Supreme Court opinion opened the door for that possibility.

“Many of us who worked in this area have been waiting basically 26 years for this shoe to drop,” said Richard Lazarus, a Harvard professor with decades of experience in environmental law.

Lazarus was referring to former moderate Justice Anthony Kennedy’s comments in a Clean Water Act case that citizen suits raised “difficult and fundamental” questions about whether they improperly dilute executive power. The late conservative Justice Antonin Scalia wrote in a dissenting opinion in the same case that citizen suits turn “over to private citizens the function of enforcing the law.” He avoided explicitly saying they were constitutional.

“The court is more like Scalia’s court since he died than it ever was when he was there,” said Lazarus.

He observed that those who lost cases where Scalia dissented are rushing back to today’s court hoping for a more favorable result.

The critical issue for citizen suits is who — the government or private citizens — collects fines and has control. A person filing a citizen suit must tell the government ahead of time. The government can stop the suit if it sufficiently pursues the case itself, but its options are limited and the person suing can stay involved. Citizen suits can force compliance with the law and result in fines, which go to the U.S. Treasury.

Twenty-five states sued the Trump administration Monday over its latest tariffs, calling them a pretext for replacing import taxes the Supreme Court struck down in February.

The United States last month imposed double-digit tariffs on 59 countries and the European Union, charging that they had not done enough to crack down on imports produced by forced labor. The new tariffs took effect just as the clock ran out on temporary tariffs President Donald Trump had turned to after the Supreme Court defeat.

“After losing at the Supreme Court, the administration is once again trying to illegally raise taxes on families and businesses with a new round of tariffs,” said New York Attorney General Letitia James.

Joining New York in the lawsuit announced Monday are Arizona, California, Colorado, Connecticut, Delaware, Hawaii, Illinois, Kentucky, Massachusetts, Maryland, Maine, Michigan, Minnesota, Nevada, New Jersey, New Mexico, North Carolina, Oregon, Pennsylvania, Rhode Island, Virginia, Vermont, Washington and Wisconsin.

Trump, who argues that high tariffs will revive American manufacturing, last year overturned decades of U.S. policy that favored lower tariffs and ever-freer trade. Invoking the 1977 International Emergency Economic Powers Act, or IEEPA, he imposed double-digit tariffs on imports from almost every country, saying America’s longstanding trade deficit amounted to a national emergency.

But the Supreme Court ruled that IEEPA did not authorize tariffs. The decision forced the administration to send refunds to importers who’d paid the tariffs. Eager to make up the lost revenue, Trump turned to temporary 10% worldwide tariffs. But they expired at midnight July 24.

Now he’s tapping more durable tariffs under Section 301 of the Trade Act of 1974, which permits the president to impose import taxes and other sanctions against countries found to engage in unfair trade practices. Trump used Section 301 to impose big tariffs on China in his first term, and they survived court challenges.

Two lawsuits filed by small businesses are challenging Trump’s sweeping tariffs announced Thursday that impose double-digit levies on 60 trading partners.

The tariffs, implemented under Section 301 of the Trade Act of 1974 for what the Trump administration says is countries’ failure to prevent imports produced by forced labor, cover 99% of U.S. imports. Critics say the goal is less to prevent forced-labor imports and more to replace the worldwide tariffs that Trump imposed last year that were struck down by the Supreme Court in February. They came just as temporary 10% worldwide tariffs — that had also been challenged in court — expired.

Educational toy company Learning Resources, which was part of the tariff lawsuit that won in the Supreme Court, filed a new suit along with several other small businesses in the Court of International Trade on Friday over the current round of tariffs.

The second lawsuit was filed by Burlap and Barrel, a New York-based spice company, and Collective Horology, a watch retailer based in Ventura, California. They are represented by Liberty Justice Center, a libertarian advocacy group.

Both lawsuits argue that the government didn’t adequately establish its case against each specific economy or spell how the tariffs will eliminate the specified practice they are being levied for, as required by Section 301.

“Forced labor is morally indefensible, but an important objective does not give the government permission to ignore the law,” said Sara Albrecht, chairman and CEO of the Liberty Justice Center. “The administration allowed one global tariff to expire and immediately replaced it with another under a different statute. Changing the statute doesn’t change the law.”

The White House did not immediately respond to a request for comment.

Experts say it might be tougher to successfully challenge the current round of tariffs than previous rounds. Trump used Section 301 to impose big tariffs on China in his first term, and they survived court challenges.

Unlike the Section 122 levies that expired Friday, “these tariffs will be with us for the long haul,” said lawyer Patrick Childress, a partner at Holland & Knight and a former U.S. trade official.

Even if countries enact the precise policies the U.S. wants, he said, they will still need to prove that they’re enforcing them to Washington’s satisfaction before the tariffs are removed. “This suggests that no short-term path for country-wide relief from the new Section 301 tariffs will be available.”