The Environmental Protection Agency violated federal laws by installing a $43,000 soundproof phone booth in the office of agency chief Scott Pruitt, a government watchdog said Monday.

The announcement from the Government Accountability Office comes as Pruitt is under fire for his use of taxpayer funds, renting an apartment tied to an energy lobbyist and allegedly retaliating against EPA staff for questioning his decisions.

The equipment in question, a secure communications booth that cost $43,238.68, was first reported last year and became an early symbol of EPA's high spending under Pruitt.

The GAO now said the purchase violated the Financial Services and General Government Appropriations Act, which prohibits spending more than $5,000 to furnish or redecorate the office of a presidential appointee without approval from congressional appropriations committees.

"EPA was required to notify the appropriations committees of its proposed obligation. By failing to provide such advance notice, EPA violated section 710" of the law, Thomas H. Armstrong, the GAO's general counsel wrote in a letter to lawmakers who requested the investigation.

The GAO also found the EPA violated the Antideficiency Act because it committed the funds "in a manner specifically prohibited by law."