The US supreme court has decided to hear arguments in a climate accountability lawsuit, marking the first time the high court has weighed in on such a case. The decision could potentially hinder the wave of climate litigation the US has seen in recent years.

“It’s not a good sign,” said Pat Parenteau, a professor of environmental law at Vermont Law and Graduate School.

The lawsuit in question was filed by the city of Boulder, Colorado, against two major oil companies: Suncor Energy USA and ExxonMobil Corporation. After Colorado’s supreme court refused to dismiss the lawsuit, the defendants filed a petition with the US supreme court asking them to shut down the case, arguing that it is pre-empted by federal laws.

If the supreme court rules against the defendants, that could be boon for climate accountability cases, allowing not only the city of Boulder but also those who have launched similar cases to breathe a sigh of relief. It could also inspire other governments to file similar litigation.

“Local communities are living with the mounting costs of climate change,” said Aaron Brockett, mayor of Boulder. “The supreme court should affirm Colorado’s right to hold these companies accountable for the harm they have caused in Colorado.”

But if the justices agree with the oil companies, it could void the Boulder case – and potentially more than a dozen others that make similar claims.

“The expectation is that [the justices] are probably going to give the oil companies some kind of win,” said Parenteau.

The defendants in the case are asking the supreme court to decide if federal law should preclude the claims made in the lawsuit. The question could be complicated by a decision made by Trump’s EPA last week to repeal a foundational legal determination which gave the federal government the ability to regulate climate-warming pollution.

In reviewing the oil companies’ petition, the supreme court could decide that before weighing in, it must determine whether or not the endangerment finding repeal affects whether or not federal law pre-empts the case. Or it could proceed as though the rollback will not change the legal argument, Parenteau said.

In addition to reviewing the arguments, the supreme court justices said they would “brief and argue” whether or not they have the authority to take up the case at this time.

“Today’s announcement makes clear the justices do not agree whether the court even has the authority to hear Boulder’s case at this time,” said Alyssa Johl, vice-president of legal and general counsel at the Center for Climate Integrity, a non-profit which tracks and supports the climate accountability cases. “The court should uphold what the Colorado supreme court and others have made clear: communities like Boulder have the right to seek accountability in their state courts when corporations have knowingly caused local harms.”

If they decide they do not have the jurisdiction to do so, the petition could be dismissed, emboldening the plaintiffs.

“This is an unprecedented situation,” Parenteau said. “I don’t know how they’re going to handle this.”

But in the meantime, the court’s decision to take up the petition at all could slow all climate accountability cases’ proceedings toward trial as courts around the country await the supreme court’s decision.

“At a minimum, it’s going to freeze all these cases, because the state courts are going to say, ‘why should we go to the trouble of having trials in these cases if, in fact, the supreme court might throw them all out,’” Parenteau said.

In recent years, US states, cities and other subnational governments have brought lawsuits against big oil for allegedly deceiving the public about the planet-heating nature of their products. The most recent government to join the wave of litigation was the state of Michigan, which filed a federal antitrust lawsuit against BP, Chevron, Exxon Mobil, Shell and the nation’s biggest fossil fuel lobby group, American Petroleum Institute.

Last year, the supreme court denied a plea to kill a Honolulu lawsuit, and turned down an unusual attempt by red states to block the cases.