California hit with threat over 'dirtiest air'

California will lose federal funding for the state's highways if it fails to tackle the worst air pollution in the United States, the county's Environmental Protection Agency said.

California Governor Gavin Newsom, a Democrat, called the EPA warning "pure retribution".

"We won't be intimidated by this brazen political stunt," he said.

In a letter dated on Tuesday to the California Air Resources Board, EPA Administrator Andrew Wheeler said that California has more than 34 million people living in areas that don't meet federal air pollution standards for pollutants like soot and smog - "more than twice as many people as in any other state in the country".

The EPA said it will give California until Oct 10 to rescind its "incomplete" plans and resubmit new reports addressing 82 municipalities facing noncompliance.

Failure to do so will result in triggering "sanctions clocks" under the law that would penalize the state with cuts to highway funding and allow the federal government to impose an implementation plan of its own.

California receives more highway funds than any other state. It is projected to get more than $19 billion from the Federal Highway Administration between the 2016 and 2020 fiscal years.

The state 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 doesn't submit an acceptable plan or implement the measures set out in it.

"The White House has no interest in helping California comply with the Clean Air Act to improve the health and well-being of Californians," Newsom said in a statement on Tuesday. "We won't go back to the days when our air was the color of mud."

The move by the EPA is the latest by the administration of President Donald Trump against the state. Last week it said it would revoke California's legal authority to set its own auto-emissions standards. California then sued the Trump administration and was joined by nearly two dozen other states.

California's leaders have attempted to get around the administration, negotiating their own agreement with automakers to voluntarily lower emissions on new cars built through 2026. Four manufacturers have joined the agreement: Ford, Honda, BMW and Volkswagen.

A top EPA official stressed that the letter wasn't a form of retaliation, the news website The Hill reported without naming the official.

AP and Reuters contributed to this story.