The House Energy and Commerce Committee launched an investigation Thursday into whether the Environmental Protection Agency’s air policy chief and his deputy have improperly aided their former industry clients since joining the administration.

Three of the panel’s top Democrats — Chairman Frank Pallone Jr. (N.J.) and two subcommittee chairs, Paul D. Tonko (N.Y.) and Diana DeGette (Colo.) — sent nine separate letters to businesses affiliated with Bill Wehrum, assistant administrator for the EPA’s Office of Air and Radiation, and with the office’s senior counsel, David Harlow. Both men worked at the law firm Hunton & Williams, now Hunton Andrews Kurth, and represented several power plant operators that EPA regulates.

Citing news reports in The Washington Post and other outlets, the lawmakers are demanding new details about the Utility Air Regulatory Group, an umbrella organization that Wehrum had represented and that is funded by several companies opposed to stricter limits on pollutants from coal-fired plants. Under Wehrum’s tenure, the EPA has sought to loosen federal restrictions on coal plants’ emissions of carbon dioxide and other pollutants.

“William Wehrum and David Harlow appear to be undermining the Clean Air Act from within EPA using the same failed rationales and legal justifications they advocated when they ran UARG,” Pallone said in a statement, referring to the two officials’ former client. “This group has operated in the shadows for far too long, and we intend to get answers.”

Noting that the committee is responsible for overseeing the EPA’s implementation of the Clean Air Act, the lawmakers wrote to Hunton’s managing partner, “As such, we are deeply troubled by several reports of unethical behavior by EPA officials, particularly in the Office of Air and Radiation.”

In letters to the firm as well as eight power companies that belong to the Utility Air Regulatory Group, the lawmakers say that the agenda of Wehrum’s office “appears remarkably similar to the substantive agenda advanced” by the organization that the EPA assistant administrator used to represent in private practice.

In an email, EPA spokesman James Hewitt said, “EPA has not received a similar letter from Congress today,” adding that Wehrum and Harlow have both taken steps to avoid any conflict of interest with DTE Energy, a client of their former firm. “Since Bill Wehrum and David Harlow started at EPA, they have both been recused from all particular matters where DTE is a party,” Hewitt said.

Wehrum, who at times has interpreted federal ethics rules himself rather than relying solely on advice from EPA ethics staff, has repeatedly denied any wrongdoing in connection with his former firm and clients. He has described the agency’s effort to scale back Obama-era limits on greenhouse gas emissions and other pollutants as in line with the Trump administration’s deregulatory agenda.

“I have, from day one, tried to be absolutely strict and assiduous as to what I do about complying with my ethical obligations,” Wehrum said in an interview with The Post in February, “because it doesn’t do me any good, and it doesn’t do the agency any good, to be doing things that people see as unethical.”

In February, The Post reported that on at least two occasions, Wehrum’s activities at EPA raised serious questions about his compliance with the Trump ethics pledge, which requires political appointees to recuse themselves from specific matters involving their former employers and clients for two years. If an appointee does meet with a former client, the pledge dictates that the gathering should be open to all interested parties — a requirement that has been interpreted to mean four other participants who were not clients.

In one instance, Wehrum weighed in on an EPA directive that had direct legal implications for a major utility, DTE Energy, which was represented by his former firm in a case against the agency. Harlow, who had represented DTE Energy just before joining EPA, also participated in conversations about the policy directive. Wehrum acknowledged that he provided input for the memo, which was timed to come out just before the Supreme Court decided whether to hear DTE’s appeal, but he said staffers redacted portions of it that posed a potential conflict.

Wehrum also met on Dec. 7, 2017, with the Utility Air Regulatory Group, along with Duke Energy, another former client, and three other utilities at his old firm. That gathering appears to violate the pledge’s requirement that such meetings must be open to all interested parties.

In late February, Pallone, along with Democratic Sens. Sheldon Whitehouse (R.I.) and Thomas R. Carper (Del.) — asked the EPA’s Office of Inspector General to investigate Wehrum’s and Harlow’s conduct.

More broadly, the panel is investigating whether Wehrum and Harlow improperly advanced the objectives of the utility group and its members. In May 2017, just six months before Wehrum joined the agency, he invited then-EPA official Mandy Gunasekara to brief the group at his law firm “on any Clean Air Act regulatory issue that you are willing and able to address,” according to emails released under a Freedom of Information Act request. And a month later, according to a document first obtained by Politico, Wehrum convened the Utility Air Regulatory Group for a meeting at which he and his colleagues at Hunton requested $8.2 million for work related to the EPA.

In addition to asking Wehrum and Harlow’s former firm to provide material, lawmakers sent letters requesting documents to American Electric Power; Ameren Corporation; DTE Energy; First Energy; Southern Company Services; the Tennessee Valley Authority; the Tri-State Generation and Transmission Association; and Vistra Energy. All eight utilities belong to the Utility Air Regulatory Group.