Governors' Biofuels Coalition

President-elect Donald J. Trump is expected to revoke permission soon after taking office, part of his pledge to scrap Biden-era climate policies. “California has imposed the most ridiculous car regulations anywhere in the world, with mandates to move to all electric cars,” Mr. Trump has said. “I will terminate that.”

The state is expected to fight any revocation, setting up a consequential legal battle with the new administration.

“California has long led the nation in pioneering climate policies and innovation,” said Gov. Gavin Newsom, a Democrat, earlier this year. “Those efforts will continue for years to come.”

Under the 1970 Clean Air Act, the Environmental Protection Agency has for decades allowed California, which has historically had the most polluted air in the nation, to enact tougher clean air standards than those set by the federal government. Federal law also allows other states under certain circumstances to adopt California’s standards as their own.

The waiver can be used to rein in toxic, smog-causing pollutants like soot, nitrogen dioxide and ozone that lead to asthma and lung disease. But California officials have also been using the waiver to curb greenhouse gases like carbon dioxide, a chief cause of global warming. Gas-powered cars and other forms of transportation are the biggest source of carbon dioxide generated by the United States.

News of the expected waiver was first reported by The Washington Post.

The brewing clash is the latest front in the battle Mr. Trump has waged against climate policies, electric vehicles and the state of California. It also exemplifies the new world of regulatory whiplash, in which policies that can make or break major industries endlessly shift back and forth.

As the fifth-biggest economy in the world, California exerts significant market influence. In recent years, other states have adopted California’s limits on tailpipe pollution, and together they make up nearly half the U.S. auto market. Similar policies have since been put in place by the European Union and Canada. The rules have helped compel automakers to invest heavily in developing and selling electric vehicles.

All of that has made California’s policies a target for Mr. Trump, who dismisses climate change as a “hoax” and says government support for electric vehicles hampers the ability of Americans to drive the car of their choice. Mr. Trump has also enjoyed financial backing from the oil and gas industry, which sees electric vehicles as a threat.

On Friday, the Supreme Court agreed to consider whether business groups have the legal standing to challenge the legality of California’s use of the waiver program to control carbon dioxide.

“California is at the front and center of pushing transportation emissions to zero,” said Ann Carlson, who helped craft the Biden administration’s policies to cut tailpipe emissions and now teaches law at the University of California, Los Angeles. “If Trump denies California the ability to issue these regulations, he is stabbing at the heart of California’s ability to clean up greenhouse gases. This would cut the knees out of California and other states that have aggressive climate policies that follow California’s lead.”

For the past year, Mr. Newsom has been working with other California officials to find ways to “Trump-proof” the state’s climate agenda, and to accelerate its transition to electric vehicles even as the federal government fights it.

“We could see entirely new policy actions and policy tools by California and other states that are committed to moving forward with clean cars,” said Peter Peter Slowik, an expert on vehicle emissions policy with the International Council on Clean Transportation, a nonpartisan research organization. “Some that we’ve maybe not seen yet in the United States.”

During Mr. Trump’s first term in office, California secretly struck legal agreements with four of the world’s largest automakers — Ford, Volkswagen, Honda and BMW — to reduce their tailpipe emissions according to limits set by the state.

All that has propelled California to become a leader in electric vehicle adoption. The top five cities in the United States with the highest numbers of registered electric vehicles have all been in California. In 2023, electric vehicles accounted for more than 30 percent of automobile registrations in the San Francisco Bay Area, according to S&P Global Mobility, an auto market research firm. In Los Angeles, that number was close to 25 percent. This year, California surpassed two million zero-emissions vehicles sold.

“The car manufacturers that struck the deal with California have already made the investments in the supply of E.V.s, and California and the other states can still find ways to create demand,” said Margo Oge, who served as the top vehicle emissions regulator at the E.P.A. under three presidents.