The United Auto Workers (UAW) will tell Congress on Thursday the union opposes the Trump administration's proposal to freeze fuel efficiency requirements at 2020 levels through 2026, according to written testimony.

The UAW's legislative director, Josh Nassar, will tell two subcommittees of the U.S. House Energy and Commerce Committee that the union, which represents workers at General Motors Co., Ford Motor Co. and Fiat Chrysler Automobiles NV, shares automakers' concerns the proposal "could lead to protracted litigation and uncertainty in the industry that will limit growth."

California and 17 other states have vowed to sue to block any freeze of the emissions requirements.

Deputy National Highway Traffic Safety Administrator (NHTSA) Heidi King told the U.S. Senate Commerce Committee on Wednesday that existing fuel efficiency standards have hiked the cost of new vehicles and may "discourage consumers from replacing their older car with a newer car that is safer, cleaner and more fuel efficient."

King said NHTSA and the Environmental Protection Administration are reviewing more than 650,000 comments and plan to issue a final rule "soon." King and Bill Wehrum, the EPA's assistant administrator for air and radiation, will testify on Thursday at the House hearing.

The Trump administration's "preferred alternative" would increase U.S. oil consumption by about 500,000 barrels a day by the 2030s but reduce automakers’ regulatory costs by more than $300 billion, the two agencies contend.

Mary Nichols, who heads the California Air Resources Board, will also testify Thursday on a separate panel. She will say that the Trump proposal "will cost Americans millions more in fuel costs, kill jobs upon which Americans depend, pump smog pollution into the air at special risk to children and the elderly, undermine the auto industry and worsen the climate crisis," according to written testimony.

Her agency estimates "the net cost of the federal rollback nationally at $168 billion."

Earlier this month, 17 major automakers including GM, Volkswagen AG and Toyota Motor Corp, urged the White House to resume talks with California to avoid a lengthy legal battle. Automakers backed a compromise, warning that the lack of a deal could lead to "an extended period of litigation and instability."

The car companies urged a compromise "midway" between the Obama-era standards that require annual decreases of about 5% in emissions and the Trump administration’s proposal.

Nassar will say that the UAW urged California, the White House and others "to develop balanced regulations that are good for the environment, American workers, U.S. manufacturing, and the economy."

David Friedman, a former deputy NHTSA administrator under President Barack Obama who is a vice president at Consumers Reports, will testify on Thursday that "automakers have the technology to make better, safer, more efficient vehicles, and federal agencies should strengthen the current standards to save Americans' money."