The Trump administration is threatening to withhold highway funding from California over its air pollution — the latest move in a political showdown as the state fights to keep tougher vehicle emissions standards.

The Environmental Protection Agency (EPA) has rolled back the tougher standards California is fighting to keep, spurring a lawsuit from California and 23 other states on Friday.

In a letter to California leaders, EPA Administrator Andrew Wheeler Andrew WheelerOvernight Energy: Trump officials finalize plan to open up protected areas of Tongass to logging | Feds say offshore testing for oil can proceed despite drilling moratorium | Dems question EPA's postponement of inequality training Democrats question EPA postponement of environmental inequality training OVERNIGHT ENERGY: California seeks to sell only electric cars by 2035 | EPA threatens to close New York City office after Trump threats to 'anarchist' cities | House energy package sparks criticism from left and right MORE said the state owes the agency an urgent turnaround on a backlog of air pollution plans.

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“Since the 1970s, California has failed to carry out its most basic tasks under the Clean Air Act. California has the worst air quality in the United States,” Wheeler wrote, saying the state has 34 million residents breathing air that does not meet National Ambient Air Quality Standards.

The letter was first reported by the Sacramento Bee late Monday.

Wheeler said the state has 130 outdated plans across various regions, some of which date back decades. He gave the state until Oct. 10 to respond and floated withholding federal highway funds.

“We certainly want to avoid these triggers, but our foremost concern must be ensuring clean air for all Americans,” Wheeler wrote.

California officials pushed back on Wheeler's letter, which they saw as retaliation against the state.

“The White House has no interest in helping California comply with the Clean Air Act to improve the health and well-being of Californians," Gov. Gavin Newsom Gavin NewsomOVERNIGHT ENERGY: California seeks to sell only electric cars by 2035 | EPA threatens to close New York City office after Trump threats to 'anarchist' cities | House energy package sparks criticism from left and right California seeks to sell only electric cars by 2035 EPA head questions connection of climate change to natural disasters MORE (D) said in a statement to The Hill. "This letter is a threat of pure retaliation. While the White House tries to bully us and concoct new ways to make our air dirtier, California is defending our state’s clean air laws from President Trump Donald John TrumpFederal prosecutor speaks out, says Barr 'has brought shame' on Justice Dept. Former Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick MORE’s attacks."

"We won’t go back to the days when our air was the color of mud. We won’t relive entire summers when spending time outside amounted to a public health risk. We won’t be intimidated by this brazen political stunt,” Newsom added.​

"EPA has unclean hands: It sat on these documents for years and is now pounding the table about paperwork issues of its own creation. We will continue to do work with EPA on its backlog, but EPA also needs to do its job and protect air quality. California and other states had to go to court, repeatedly, to get the EPA to implement the strict smog standards it claims to be worried about," said California Air Resources Board Executive Officer Richard Corey.

"This letter appeared only days after EPA attacked our state authority on cars, increasing air pollution while at the same time limiting our ability to reduce it. If the Trump administration is serious about air pollution it will reconsider revoking our waiver, and while they’re at it, why not also fund the EPA to review submitted documents in less than a decade.”

At the heart of the fight is California's authority to set its own more stringent vehicle emissions standards, which was first granted by the Obama administration. The Trump EPA, though, moved to revoke the waiver that allowed California to set its own tougher pollution rules for roughly 50 years. That led California and other states to sue.

The more stringent vehicle emissions standards California is fighting to keep are tied to its efforts to clean the state’s air. The state is also in the midst of an effort to strike a deal with automakers to produce more fuel-efficient vehicles even as the Trump administration moves to roll back higher fuel efficiency goals set under Obama.

“The standards that we are now in the process of enforcing are necessary to protect the public health and welfare, not just because we care about the future of the planet or polar bears, it's because we actually need these extra clean cars in order to meet the health standards that are set by the federal government that we violate now on a very regular basis throughout Southern California and the San Joaquin Valley," California Air Resources Board Chairwoman Mary Nichols said in a recent press conference announcing the state’s intent to fight the Trump rollbacks.

While California said it will fight to preserve states’ rights, now at risk for the state is some $19 billion in transportation funding it is projected to receive from the 2016 to 2020 budgets.

In a call with reporters to discuss Wheeler’s letter, a top EPA official stressed the move was not a form of retaliation.

“Yesterday’s letter is unrelated to last week’s announcement” that the EPA would revoke California’s waiver, the official said. “This is related to California’s continued inability to carry out or attain basic requirements under the Clean Air Act.”

The official said the EPA may send similar letters to other states, but could not list other states that also had a high number of backlogged plans, saying only that California represented a disproportionate share.

“There’s a strong reason for the focus here. If you’re in a hole the first thing is to stop digging,” he said.

California doesn’t have to meet the air quality standards to keep receiving highway funding, but the EPA could move to withhold funds if the state does not submit an acceptable plan or implement the measures set out in it.

Highway funding can be withheld 24 months after the EPA has determined the state efforts are inadequate unless Wheeler takes action to fast-track the process.

Environmental groups also blasted the EPA's move.

John Walke, clean air director for the Natural Resources Defense Council, said it’s hypocritical for the EPA to take away tools California needs to improve its air quality while rolling back other regulations designed to curb pollution.

Walke also questioned EPA’s decision to ask California to withdraw its old plans when EPA has the power to reject the plans outright.

“Merely raising the specter of highway funds withdrawn is brute political force but California is shrewd and is not going to buckle in the face of their bluff,” he said. “Disapproval requires hundreds of hours of his staff to figure out what should be disapproved for plans that have been in EPA offices for years or even decades in some cases.”

Miranda Green contributed reporting.

Updated at 3:55 p.m.