When President Donald Trump on Thursday blocked California’s first-in-the-nation rule banning the sale of new gas-powered cars by 2035, he also stopped Colorado’s requirement that 80% of all vehicle sales in this state be electric by 2032.

Colorado, which had adopted California’s rules two years ago, quickly joined California and nine other states in a lawsuit to challenge the move.

Trump signed a resolution that was approved by Congress last month that aims to quash the country’s most aggressive attempt to phase out gas-powered cars, which are a leading source of greenhouse gas emissions in the country. Trump also signed measures to overturn state policies that curb tailpipe emissions in certain vehicles and smog-forming nitrogen oxide pollution from trucks.

“The Trump administration’s attack on clean air is breathtaking,” Colorado Attorney General Phil Weiser said in a news release announcing the lawsuit. “We’re in court to defend Colorado’s cost-effective clean car program, which was implemented to improve air quality, reduce harmful ozone pollution, and increase choices that Coloradans have when purchasing an electric vehicle.”

The Colorado Air Quality Control Commission partially adopted California’s rules in 2023, which was allowed under the Environmental Protection Agency’s regulations.

In Colorado, the clean cars standards would have required auto manufacturers to make and sell more electric vehicles starting with model year 2027 and increasing each year until 2032, when 82% of all vehicles sold in the state were to be electric. The standard also required new conventional cars and passenger trucks to lower tailpipe emissions.

Colorado’s adoption of California’s Advanced Clean Truck standards also required medium- and heavy-duty truck manufacturers to sell an increasing percentage of zero-emission vehicles starting in 2027.

Colorado also adopted California’s Heavy-Duty Low Nitrogen Oxides rule requiring heavy-duty truck manufacturers to make cleaner heavy-duty trucks for sale or lease in this state starting in 2027.

Colorado’s clean cars rule was not as stringent as California’s because it did not block all sales of gas-powered vehicles.

Still, the state is pushing zero-emission vehicles as it strives to eliminate almost all greenhouse gas emissions by 2050. Gov. Jared Polis has said he wants more than 2 million electric cars and trucks on the roads by 2035.But Colorado will not be able to enforce its rules if the California standards are blocked by the president.

Transportation is the leading cause of greenhouse gas emissions, and cars and trucks account for 80% of those transportation emissions. Greenhouse gases such as carbon dioxide build up in the atmosphere, trapping heat and causing global warming. Those rising temperatures are responsible for droughts, hotter summers and more intense wildfires in Colorado.

The pollution also creates ground-level ozone when nitrogen oxides and volatile organic compounds — emissions from vehicles — bake in the heat and form a brown smog over the Front Range. That ozone pollution is an ongoing challenge for the Front Range, which is in severe violation of federal air quality standards. It also makes people sick.

Electric cars have proven to be popular in Colorado.

Electric vehicles made up 25.3% of new vehicles sold in the state in the third quarter of 2024, placing Colorado ahead of California in EV sales. The state has also been investing in infrastructure to support the rising popularity.

The Republican rollback of California’s rules, the proposed elimination of federal tax credits for EV purchases, and tariffs on automakers throw chaos into the auto market and environmental efforts, Will Toor, executive director of the Colorado Energy Office, said last month in an interview with The Denver Post.