SAN FRANCISCO (CBS SF) — The Trump Administration is threatening to freeze California’s federal highway funds in the latest clash over air quality and climate change.

A letter from the EPA to the California Air Resources Board (obtained by the Sacramento Bee ) accuses California of failing to comply with the Clean Air Act. The letter alleges that the state failed to submit air pollution control plans.

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California governor Gavin Newsom fired back Monday evening, saying the White House is trying to “bully” California as the state defends its clean air laws “from President Trump’s attacks.”

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“The White House has no interest in helping California comply with the Clean Air Act to improve the health and well-being of Californians. This letter is a threat of pure retaliation,” Newsom said in a statement.

“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.”​​

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The threat comes after the state sued the administration for revoking its authority to set more stringent vehicle emissions standards.