Environmental Protection Agency Administrator Scott Pruitt testifies before a House Appropriations subcommittee in April. (Ricky Carioti/The Washington Post)

The U.S. Office of Special Counsel is investigating whether Environmental Protection Agency Administrator Scott Pruitt retaliated against staffers who questioned his spending and management decisions, according to three individuals familiar with the probe.

During Pruitt’s tenure, the EPA has reassigned or taken administrative action against several career officials and one political appointee who had objected to the way he was spending taxpayer funds or using the perks of his office, these individuals said.

Attorneys from the Office of Special Counsel, which responds to whistleblower complaints from federal employees and can choose to prosecute cases, is in the process of speaking to a half-dozen current and former employees as part of the case, according to Kevin Chmielewski, Pruitt’s former deputy chief of staff operations. The office is taking the matter “extremely seriously,” Chmielewski said in an interview Monday.

Politico first reported the probe was underway. Pruitt is facing more than a dozen federal inquiries into his spending and management decisions, including review of his first-class travels, installation of a $43,000 soundproof phone booth in his office and his $50-per-night condo rental from a Washington lobbyist.

Chmielewski, a Trump appointee who has said publicly he was fired in February after questioning Pruitt’s decision to routinely fly first-class and spend money on a range of security-related matters, said he spent at least six hours speaking to officials from the special counsel’s office on Thursday. The office has assigned three attorneys to review claims he and other EPA officials have made, Chmielewski added.

In April, Pruitt denied any retaliation during a pair of hearings on Capitol Hill, during which Rep. Betty McCollum (D-Minn.) alleged “staff has been under attack during your tenure” and “there’s documented retaliation, as far as I’m concerned.”

Pruitt has attributed many of the most controversial spending decisions at the agency to his aides and said the decision to travel first-class and receive round-the-clock protection stemmed from threats he has received as administrator.  He responded to McCollum, “I would say to you unequivocally I know of no instance — I’m not aware of any instance that any employment action has been taken against someone for any advice or counsel they’d given with respect to spending.”

Neither the Office of Special Counsel nor the EPA would comment on the matter Monday. OSC spokesman Zachary Kurz said in an email the office “cannot comment on or confirm any open investigations,” and EPA spokesman Jahan Wilcox said in a separate email “EPA does not comment on matters involving OSC.”

The other agency officials who either were reassigned or took leaves from the agency include former deputy chiefs of staff John E. Reeder and Reginald E. Allen; security agents John C. Martin and Eric Weese; and Mario Caraballo, deputy associate administrator of the EPA’s Office of Homeland Security. Reeder is married to Washington Post reporter Carol Leonnig.

Caraballo, who submitted a report questioning the grounds for the administrator’s 24/7 security detail, was placed on administrative leave earlier this year and has since retired.

Chmielewski said while Pruitt’s top aides “thought they were going to pressure me into resigning” and compiled paperwork to that effect, he was actually fired.

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For Pruitt, gaining Trump’s favor — and keeping it — came through fierce allegiance