The Trump administration has warned the state of California that it will face consequences if it fails to submit plans addressing what the Environmental Protection Agency called the "worst air quality" of any state in the country, according to a Monday letter from the agency.

The letter from EPA administrator Andrew Wheeler states that 34 million people in California are living in areas that don't meet federal air quality standards, a number twice as large as any other state in the country. It further states the plans California has submitted to the EPA, known as State Implementation Plans (SIPs), to address areas with inadequate air quality "have fundamental issues related to approvability" and must be resubmitted.

The letter informs California that if it fails to submit new plans to increase air quality, the state would be ineligible to receive billions of dollars it is otherwise projected to get from the Federal Highway Administration.

"We certainly want to avoid these statutory triggers, but our foremost concern must be ensuring clean air for all Americans," Wheeler says in the letter. "That is our goal."

The letter gives California until Oct. 10 to notify the EPA whether it plans to withdraw and resubmit the SIPs. The federal government could impose its own plan on California if it fails to get new SIPs approved. Wheeler expressed hope that California will work with the Trump administration to address its failures.

"California has failed to carry out its most basic responsibilities under the Clean Air Act, and as a result, millions of Californians live in areas that do not meet our nation's air quality standards," he said in a statement on the letter. "EPA stands ready to work with California to meet the Trump administration's goal of clean, healthy air for all Americans, and we hope the state will work with us in good faith."

Wheeler told McClatchy‘s Michael Wilner past administrations allowed California to avoid consequences for its failure to submit air quality plans to the EPA.

Wheeler only learned this summer of a giant backlog of SIPs, including more than 130 unprocessed plans from California alone. He was told the backlog resulted from previous administrations' unwillingness to deny plans from California due to the harsh penalties tied to a failing grade from the EPA.

"When I learned about this a couple months ago, the question I asked the staffer was, ‘why are we holding on to these—why haven't we acted?'" Wheeler said. "And the response I got back was, ‘we didn't want to deny them and they couldn't approve them.' Well that's ridiculous to allow 34 million people to live in areas not in compliance with our air standards."

The agency says the plans it currently has on file from California fail to meet the "minimum threshold of public health protection necessary for approval." The EPA also says it's prepared to put together plans for California itself if the state declines to cooperate.

"As a first step, EPA is calling on California to immediately withdraw inactive SIPs that would most likely be denied," the agency said. "If California does not withdraw the inactive SIPs in a timely manner, EPA will begin the process of evaluating these SIPs for disapproval and developing Federal Implementation Plans that are approvable and will protect public health."