What to know about the US Senate’s effort to block vehicle-emission rules in California

SACRAMENTO, Calif. — Congress may stop California from implementing its first-in-the nation rule banning the sale of new gas-powered cars by 2035.

A Senate vote expected as soon as this week could end the nation’s most aggressive effort to transition toward electric vehicles as President Donald Trump’s administration doubles down on fossil fuels.

California makes up roughly 11% of the U.S. car market, giving it significant power to shape purchasing trends. Vehicles are one of the largest sources of planet-warming emissions.

The Republican-controlled Congress is targeting three California waivers that set stricter emissions rules than the federal government. The House voted to block them several weeks ago, and Senate Majority Leader John Thune said his chamber would take up a similar effort this week, even though the Senate Parliamentarian and the U.S. Government Accountability Office say California’s policies are not subject to the review mechanism used by the House.

Thune said California’s “are an improper expansion of a limited Clean Air Act authority and would endanger consumers, our economy, and our nation’s energy supply.”

California Gov. Gavin Newsom and state air regulators say what lawmakers are doing is illegal and they will likely sue if the measure advances.

Here’s what to know:

The Environmental Protection Agency has let the state adopt stricter emissions standards for decades, and other states can sign on to those rules.

California has some of the nation’s worst air pollution, and the waivers date back to efforts in the 1960s and 1970s to fight smog in Los Angeles.

Trump rescinded California’s ability to enforce its standards during his first term, but President Joe Biden’s administration restored it in 2022.

Newsom, a Democrat, announced plans in 2020 to ban the sale of new gas-powered cars by 2035. State air regulators formalized the rules in 2022, and the federal government allowed them to move forward last year.

The rule requires automakers to sell an increasing number of zero-emission cars, pickup trucks and SUVs over the next decade. Electric vehicles would have to make up 43% of new sales by 2027, 68% by 2030 and 100% by 2035. People would still be able to buy used gas-powered cars, plug-in hybrids or hydrogen-powered vehicles.

California passed another rule in 2020 to phase out the sale of medium- and heavy-duty diesel vehicles, including box trucks, semitrailers and large pickups. Depending on class, zero-emission trucks…