A group of California Democrats on Monday pressed the EPA’s internal watchdog to investigate whether the agency has retaliated against their state for political reasons, including by threatening to withhold federal funds for multiple transportation projects.

EPA Administrator Andrew Wheeler threatened in a Sept. 24 letter to the California Air Resources Board, the state’s air agency, to withhold federal funding for highway projects if local regulators did not implement plans, known as “state implementation plans,” or SIPs, to improve air quality.

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In a letter Monday to Charles Sheehan, the EPA’s deputy inspector general, House Democrats requested that the IG office scrutinize whether Wheeler’s letter and its threats “are a result of undue political influence” at the agency.

Seven California Democrats — Reps. Doris Matsui, Nanette Barragán, Jerry McNerney, Anna G. Eshoo, Tony Cárdenas, Scott Peters and Raul Ruiz — sent the letter.