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A $43,000 soundproof telephone booth that Environmental Protection Agency Administrator Scott Pruitt put in his office has caused federal watchdogs to speak up loudly.

On Monday, the General Accountability Office sent an eight-page letter to Senate lawmakers reporting that the booth violated federal spending law that caps the amount a presidential appointee can spend on upgrading their office at $5,000 without notifying the appropriations committees in the Senate and House beforehand.

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GAO General Counsel Thomas Armstrong also wrote that the purchase violated the Antideficiency Act, "because EPA obligated appropriated funds in a manner specifically prohibited by law.”

Environmental Protection Agency chief Scott Pruitt listens to President Donald Trump before a Cabinet meeting on April 9. Jim Lo Scalzo / EPA

The booth — which cost $24,570 itself with nearly $20,000 more in installation costs — is part of a major security upgrade that he ordered for his office that also included biometric locks and a sweep for listening devices.

Pruitt has already come under fire from critics for his 24-hour security detail and first-class travel, both of which have been justified with security concerns.

Pruitt's EPA officials, though, had argued that the booth served a functional purpose: To allow Pruitt to receive calls from President Donald Trump "without concern that classified, deliberative, privileged or sensitive information might inadvertently be disclosed."

Armstrong's letter, however, rejected that claim that aesthetics were the only purview of the requirement of notifying Congress.

While EPA now argues there's too much energy being wasted on an investigation into the booth.

“The GAO letter ‘recognized the ... need for employees to have access to a secure telephone line’ when handling sensitive information," EPA spokeswoman LIz Bowman said in a statement. "EPA is addressing GAO’s concern, with regard to congressional notification about this expense, and will be sending Congress the necessary information this week.”