WASHINGTON (AP) — A government watchdog will examine whether the head of the Environmental Protection Agency misused taxpayer money by purchasing a soundproof booth for making private phone calls from his office.

The EPA's Office of the Inspector General confirmed the latest investigation Tuesday, following a request by congressional Democrats. It will be at least the third probe launched into EPA Administrator Scott Pruitt's actions since President Donald Trump appointed him earlier this year.

Pruitt spent nearly $25,000 on the custom-made privacy booth. He told a congressional oversight committee last week the purchase was justified because he needs a secure phone line to communicate with the White House. None of Pruitt's predecessors used a similar setup.

Pruitt said the booth serves as a Sensitive Compartmented Information Facility, known as a SCIF, which typically are secure rooms used to house computers and equipment for communicating over classified government networks. Former EPA officials have said that explanation doesn't make much sense.

There was already a SCIF at EPA headquarters in Washington where officials with the appropriate levels of security clearance can go to access classified information.

Although EPA employees rarely deal with government secrets, the agency does occasionally receive, handle and store classified material because of its homeland security, emergency response and continuity missions.

"The use of a secure phone line is strongly preferred for Cabinet-level officials, especially when discussing sensitive matters," EPA spokesman Jahan Wilcox said Tuesday. "We do not comment on OIG matters until they are resolved."

The inspector general is also looking into whether Pruitt has violated federal rules by making frequent trips that include weekend layovers at his home in Oklahoma and by urging members of the National Mining Association to tell Trump to withdraw from the Paris climate deal. Critics said Pruitt's remarks at the pro-coal group's April meeting violated anti-lobbying laws covering Cabinet officials.

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Follow AP environmental writer Michael Biesecker at http://Twitter.com/mbieseck