Attorneys representing a group of conservative states and fuel producers opposed to an Environmental Protection Agency waiver allowing states to set their own vehicle emissions standards failed to convince the U.S. Supreme Court to hear its side.

By declining to take up the challenge, the Supreme Court let stand an April decision by the D.C. Circuit of the U.S. Court of Appeals. That decision hinged on a claim that the waiver represented an unconstitutional interpretation of the federal Clean Air Act.

California has for decades set more aggressive emissions standards than those in place at the federal level. To sell vehicles in the nation’s No. 1 market, automakers have been forced to follow California’s lead; along the way, 17 other states have signed on to its stricter standards.

The Supreme Court’s inaction tees up what could be among the first decisions made by President-elect Donald Trump once he takes office in January. Trump rolled back the EPA waiver by executive order in 2019, during his first administration. President Joe Biden reinstated it in 2022.