The Environmental Protection Agency is refusing to release the written waiver that allows Administrator Scott Pruitt to fly regularly in first or business class for security reasons — a practice that sets him apart both from his predecessors and other current Cabinet members.

The agency has not spelled out why any threats against Pruitt warranted such a move, and officials would not disclose on Wednesday who approved the waiver or how long it has been in effect, saying reporters would need to file a Freedom of Information Act request for more details.

The EPA this week told reporters that Pruitt had a “blanket waiver” allowing him to bypass coach class whenever possible. Federal regulations, however, say that “blanket authorization of other than coach-class transportation accommodations is prohibited and shall be authorized on an individual trip-by-trip basis.”

On Wednesday afternoon, the agency backed away from its earlier statements, saying it actually submits the same security-related waiver for each trip.

“The [General Services Administration] has a provision for security,” EPA spokesman Jahan Wilcox said in a statement. “As such, for every trip Administrator Pruitt submits a waiver to fly in either first or business class.”

The latest scrutiny over the expensive and secretive travel habits of the EPA head and his staff comes after The Washington Post detailed this week how Pruitt’s trips have cost taxpayers hundreds of thousands of dollars.

His immediate predecessors, as well as Cabinet members from Democratic and Republican administrations, regularly sat in economy when flying commercial, as mandated by federal travel regulations. Agencies are allowed to authorize first-class travel in rare instances, such as a flight of 14 hours or more, a medical disability or when “exceptional security circumstances” mean “use of coach class accommodations would endanger your life or government property.”

Members of President Trump's Cabinet have taken noncommercial flights at the expense of taxpayers, and Trump says he's "not happy." (Monica Akhtar/The Washington Post)

A handful of Trump administration Cabinet members travel by government plane for security reasons, including the secretaries of the defense, state, homeland security and justice departments. The rest typically fly coach unless they pay for an upgrade themselves or are taking a long-haul flight.

A small number of Cabinet members — including former Commerce secretary Penny Pritzker and current Education Secretary Betsy DeVos — have covered the cost of traveling on their personal planes.

In comments this week during a visit to New Hampshire, Pruitt attributed his numerous first-class, taxpayer-funded flights to his personal security detail and chief of staff, saying he plays no role in deciding such arrangements.

“I’m not involved in any of those decisions,” he told the New Hampshire Union Leader. “Those are all made by the [security] detail, the security assessment in addition to the chief of staff.”

Asked again about his expenditures in a television interview with WMUR-TV in Manchester, N.H., Pruitt said that during his tenure at the EPA, he has had interactions with other travelers that have “not been the best.” He reiterated that his first-class travel arrangements aren’t up to him.

Agency security officials “place me on the plane where they think is best from a safety perspective,” he told the station.

While the EPA’s inspector general has said that Pruitt has received a higher number of threats than his recent predecessors, that hasn’t ended questions about why the administrator was given an open-ended waiver to fly first class using public funds.

“Pruitt’s explanation is absurd and assumes that it’s easier to protect someone in first class than in economy,” said Chris Lu, who served as White House Cabinet secretary during Barack Obama’s first term. “Members of Congress who routinely fly coach should be offended by his lavish travel habits.”

During his time managing the Obama Cabinet, Lu said no waivers for first-class travel were granted for any Cabinet member. “During a time of recession, we knew it was important to demonstrate that we were good stewards of taxpayer dollars,” he said.

A former senior administration official who served under George W. Bush and was familiar with the travel practices of Cabinet members during that administration said that “everybody flew economy, with very few exceptions.” The official spoke on the condition of anonymity to discuss security arrangements.

Pruitt has taken other security measures since assuming office a year ago. He is the first EPA administrator to have a round-the-clock security detail, and he has had a $25,000 soundproof phone booth installed in his office for making secure calls. Biometric locks also were added to its doors.

House Democrats on Wednesday asked EPA’s inspector general, who already is investigating elements of Pruitt’s travel practices, to examine his first-class flights as well as who was involved in drafting the security waiver that allows them.

“Administrator Pruitt’s many first-class flights around the country at taxpayers’ expense raise renewed concerns of secrecy and waste at the Trump EPA,” the Democratic lawmakers wrote. “American taxpayers deserve assurances that their tax dollars are not wasted by the government’s highest officials.”

White House spokeswoman Sarah Huckabee Sanders on Wednesday declined to weigh in on Pruitt’s flights, saying instead that the administration was focused only on the deadly school shooting unfolding in Florida.

Josh Dawsey contributed to this report.