The G.A.O. said it was not taking a position on whether or not the installation of the privacy booth was necessary, but was focusing only on the violations of two laws: the Antideficiency Act, which is designed to prevent spending that has not been budgeted, and the Financial Services and General Government Appropriations Act, which limits the amount political appointees may spend on office item to $5,000.

Auditors wrote that the E.P.A.’s “failure to comply with a governmentwide statutory requirement that an agency notify the appropriations committees before it spends more than $5,000 for the office of a presidential appointee” was a violation of the law and should be reported to Congress and the president.

In an eight-page letter to lawmakers, Thomas H. Armstrong, the G.A.O.’s general counsel, said the agency did not send advance notice to Congress when it paid $43,238.68 from its Environmental Programs and Management budget to pay for the installation of the soundproof booth.

The G.A.O. reports its findings to Congress but has little enforcement power of its own.

Senator Tom Udall, the New Mexico Democrat who requested the investigation along with three other members of Congress, said Mr. Pruitt was “blatantly breaking laws and ethics rules that protect taxpayers from government waste, fraud and abuse in order to help himself to perks and special favors.”

Senator John Barrasso, Republican of Wyoming and chairman of the Environment and Public Works Committee, which has jurisdiction over the E.P.A., also criticized the agency, while not identifying Mr. Pruitt by name.