President Donald Trump’s announcement on Monday that he’d nominated Brett Kavanaugh to replace retiring Supreme Court Justice Anthony Kennedy prompted rampant speculation about the future of Roe v. Wade. There was less talk, however, about Massachusetts v. EPA.

The latter ruling, which The Atlantic recently called “the most important court case in U.S. climate law,” is the reason the Environmental Protection Agency has the legal authority to regulate greenhouse gases. The Clean Air Act of 1970 requires the government to regulate air pollution—in fact, the EPA was created to implement those requirements—but in 2003 the Bush administration insisted that the law didn’t compel it to regulate greenhouses gases such as carbon dioxide. Massachusetts and many other states and cities disagreed, and sued.

When the case reached the high court, the justices narrowly ruled that greenhouse gases were indeed pollutants. Kennedy was the deciding vote, joining the court’s four liberal justices. Now, with Kavanaugh set to replace Kennedy, conservatives may have the votes to overturn that precedent.

“Just like the future of Roe v. Wade, the future of federal action to rein in climate change should be a huge issue in [Kavanaugh’s] confirmation hearing,” said Abbie Dillen, the vice president of climate litigation at Earthjustice.

Kavanaugh, a 53-year-old judge for the D.C. Circuit Court of Appeals, is “pretty consistently anti-environment on every front,” Center for Biological Diversity senior counsel Bill Snape told BuzzFeed News. That includes the issue of greenhouse gases. Kavanaugh “will not be afraid to say that greenhouse gases don’t fall into the category of pollutants the [Clean Air Act] was supposed to address,” said Brendan Collins, an environmental litigator at Ballard Spahr LLP who has argued before Kavanaugh. “He maintains a level of discomfort of anything he regards as a reach, authority-wise, from the EPA.”