Colorado has joined a coalition of states in filing a lawsuit challenging the Trump administration’s use of the Congressional Review Act to prohibit states from adopting stricter emissions standards for certain motor vehicles. 

Adopted in 1996, the Congressional Review Act allows Congress to review and overturn new federal agency regulations before they take effect. The Trump administration has invoked the law to block California’s Clean Air Act waiver, which permits the state to set vehicle emissions standards that are more stringent than federal requirements.

Several states, including Colorado, have adopted California’s emissions standards. 

According to Colorado Attorney General Phil Weiser, the Environmental Protection Agency has already ruled that Clean Air Act waivers are not reviewable under the Congressional Review Act. However, in what Weiser called a “naked attempt” to circumvent the normal review process, the current EPA has submitted the waivers to Congress for review anyway.

The lawsuit, backed by 11 attorneys general, was filed immediately after President Donald Trump signed three congressional resolutions on Thursday that will bar California’s electric vehicle sales mandates and diesel engine rules. Colorado and other states have also adopted California policies. 

Leaders of the auto industry, including Toyota and GM, lauded Trump’s actions, saying that his directives are more in line with reality.

Weiser described the president’s actions as an “assault” on states’ authority.

“Rolling back the federal Clean Air Act waivers through the illegal use of the Congressional Review Act is an assault on the authority of states, like Colorado, to adopt stronger tailpipe pollution limits than those set by the federal government,” Weiser said. “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.”

Colorado officially adopted California’s vehicle emissions standards in 2018 through an executive order by former Gov. John Hickenlooper. The standards aim to reduce the state’s greenhouse gas emissions by 26% by 2025 and require new vehicles sold in Colorado to average 26 miles per gallon. 

In 2023, Colorado enacted standards, which direct vehicle manufacturers to sell 82% electric vehicles by 2032. 

California Attorney General Rob Bonta submitted the complaint in the Northern District of California. Besides Colorado and California, other states joining the suit included Delaware, Massachusetts, New Jersey, New Mexico, New York, Oregon, Rhode Island, Vermont and Washington.