Story highlights CNN learned in October that the EPA was beefing up security measures surrounding Pruitt

Pruitt's travel spending has also come under scrutiny in recent months

Washington (CNN) The Environmental Protection Agency inspector general will look into agency spending in connection with EPA enforcement agents being used on Administrator Scott Pruitt's security detail, according to a letter sent to Rep. Peter DeFazio, the top Democrat on the House Transportation Committee.

The letter from Inspector General Arthur A. Elkins Jr. says that his office will look into "whether the EPA complied with applicable oversight controls in deciding to make the expenditures" to add security to Pruitt's security detail.

CNN learned in October that the EPA was beefing up security measures surrounding Pruitt to an unprecedented level, and members of Congress began to ask if the costs are a "potential waste or abuse of taxpayer dollars."

Pruitt's security detail was in the process of hiring a dozen more agents, a source with knowledge of the situation told CNN then, as the number of threats against the agency leader increased. The incoming agents were intended to grow the team that works in shifts to provide him around-the-clock protection, something unheard of for Pruitt's predecessors.

Pruitt's travel spending has also come under scrutiny in recent months following news reports outlining frequent trips to his home state of Oklahoma as well as several flights on charter and government aircraft. Earlier this week, the EPA Office of Inspector General announced it is expanding the time frame of its probe into Pruitt's travel. Previously, the investigation was looking at travel through September 30, 2017, and will now include travel through December 31 "based on additional congressional requests."

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