The purchase of business-class tickets was not a violation of US government policy, which allows federal employees to travel business class on trips lasting 14 hours or more.
The EPA has argued that Pruitt's personal security detail, which demands far more resources than for his predecessors and has cost taxpayers an estimated $3 million, is necessary given the intensity and number of threats he has received.
Among those scandals: He reportedly spent $25,000 on a soundproof phone booth, regularly requests per diem lodging expenses above the government's daily spending rate, rented a room in a home owned by the wife of an energy lobbyist, defied a White House in order to give two close aides massive raises and consistently flies first class in order to avoid the public shouting curse words at him.
Whitehouse asked the inspector general to probe whether Pruitt flew first class even when traveling on personal business - and if his bodyguards were seated there too. Pruitt ended up going to Corpus Christi, Texas to assess the agency's relief efforts instead.
In a letter to Whitehouse dated Tuesday, Elkins said his office would pursue an inquiry into the matter, despite time and budget constraints.
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Trump had tried to recruit at least two legal eagles in recent weeks - Emmet Flood and Theodore Olson - but both turned him down. He declined to say whether Trump has made a final decision on whether to sit for an interview with Mueller.
The trip has not been rescheduled. An EPA spokesman told Reuters that rescheduling the trip had been stymied by Australia's parliamentary schedule. An economy class ticket for the trip would have cost about $1,400.
The official spoke on condition of anonymity citing fear of retaliation.
Larry Noble, former president of the Council on Governmental Ethics Laws representing government ethics administrators, questioned whether so many staffers were required for the advance team and said Pruitt's credibility on the broader issue of spending taxpayer money was low. From unjustified first class flights, to leasing an apartment from an energy lobbyist, to freakish spending on a soundproof phone booth and bulletproof desk, to arrogant demands for a motorcade with the right to bypass D.C. traffic lights, to disciplining employees who raised questions about all this, we have had enough.
More than 130 USA lawmakers signed a companion resolution in the House.