The head of Colorado’s Department of Transportation told Congress on Thursday that an effort by President Donald Trump’s administration to freeze fuel economy standards is “a deeply flawed and ideologically driven proposal” that could compel Colorado to take legal action.

Shoshana Lew, the state agency’s executive director, testified before two House Energy and Commerce subcommittees on CAFE – corporate average fuel economy – standards for vehicles.

Those standards, first created in 1975, have trended up for decades. In 2012, President Barack Obama put in place a rule requiring they increase to 54 miles per gallon by 2025. Last year, the Trump administration proposed freezing that increase at 37 miles per gallon after 2021.

“The (Trump) proposal would increase U.S. fuel consumption by about half a million barrels per day,” Lew said Thursday. “It’s no surprise that the oil industry supports the proposed flatline.”

The Trump administration also proposed eliminating a waiver that has, for decades, allowed California to set standards more stringent than the federal government’s fuel standards. In written remarks Thursday, Lew said Colorado will fight the Trump administration “in the courts, in partnership with California and many other states,” if the proposed change is finalized.

In February, Colorado signaled its support for California’s legal actions, but it has not joined a lawsuit against the Trump administration. Meanwhile, the state is being sued by auto dealers after a state board adopted more stringent fuel emission standards last year. That case is pending.

Heidi King, deputy administrator for the National Highway Traffic Safety Administration under Trump, argued the freeze in fuel standards will keep car and truck prices reasonable, ultimately getting more inefficient clunkers off American roads and highways and improving air quality.

“We know that consumers are less likely to replace their older, less safe car with a newer, safer car if that newer, safer car is 20 percent more expensive,” King told members of Congress.

Some Republicans argued the Obama-era standards were unwanted interference in the auto market, shoving consumers toward hybrid cars and small vehicles rather than those they want.

“We like big things. We like big trucks. We like big engines,” said Rep. John Shimkus, a southern Illinois Republican. “We like to haul trailers … to haul horses and feed and hay and all those things that have to happen in rural America.”

Lew took over CDOT in February after holding several positions in Obama’s U.S. Department of Transportation. On Thursday, she was a steadfast defender of the former president’s fuel emission standards, a pillar of his environmental legacy, as well as Colorado’s own environmental work.

“We believe it is the right time for bold, aggressive and pragmatic action to achieve a cleaner transportation sector,” she said. “Indeed, we are encouraged to see bipartisan collaboration in our own legislature, and cooperation between state and local government partners across Colorado.”