The senators said they have reviewed documents that say the U.S. Secret Service found no "behaviors of interest" against Pruitt – indicating there was not a credible threat against him.
"It is hard to reconcile the public statements of EPA, and the President, with these internal and external assessments," Whitehouse wrote.
“They released information that should not have been released. They selectively chose information," Barrasso told ABC News on Tuesday. "It’s why we are not going to have hearings that they have suggested. They’ve really gone way beyond what should be done in terms of sensitive documents related to security of a cabinet official.”
The EPA has said that Pruitt has faced a torrent of threats during his tenure citing a threat assessment from the inspector general that found that there have been more threats and some serious threats against Pruitt than previous administrators.
“Scott Pruitt has faced an unprecedented amount of death threats against him,” EPA spokesman Jahan Wilcox said in an email Tuesday, saying that threats are assessed by EPA's enforcement and homeland security offices as well as the protective detail.
“Americans should all agree that members of the President’s cabinet should be kept safe from these violent threats,” he said in the statement.
The EPA's inspector general has been looking into the cost of Pruitt's 24-7 security detail and whether the agency followed all agency rules in assigning the detail. That report is expected to be published this summer. The inspector general's office evaluates threats against the administrator and other EPA employees but does not make day-to-day decisions about how they should be protected.
"A closer look at the description of many of these threats cast doubt that they appropriately justify the kinds of security measures Mr. Pruitt has sought," they wrote.
The letter also says that none of the incidents in the internal documents concerned air travel and that the only threat being prosecuted was directed at both Pruitt and McCarthy.
The EPA has said that Pruitt often flies first class because it was recommended by his security team, saying that the agency grants him a waiver to fly an upgraded class every time because of the security threats. According to the letter, the February memo from EPA's Office of Homeland Security Office found that the justification for those first-class flights "mischaracterized" threats and that EPA intelligence has "not seen any analysis to indicate why the Administrator would be at any greater risk on a commercial airline than any other passenger."
Pruitt said in an interview with Fox News last week that his security detail wanted him to fly in first class so that he could be evacuated more quickly if there was a problem. He told CBS News last month that he has directed his staff to find a new approach that would involve more flights in coach.
His security appeared to be on track to reach an estimated $3 million since he took office, as reported by the Associated Press, more than twice the cost of security for former administrator Gina McCarthy. EPA documents obtained by E&E News found that the EPA spent more than $830,000 on payroll and travel for Pruitt's security detail in his first four months in office, compared to about $465,000 for McCarthy's detail in her first few months.
The EPA also spent around $43,000 to install a "secure phone booth" in Pruitt's office and has swept his office for bugs and installed biometric locks on his office. The Government Accountability Office, known as the congressional watchdog, is looking into the cost of the phone booth.
Whitehouse has also asked for more information about the contract to sweep Pruitt's office for bugs because the company that was hired to do the sweep was connected to the head of Pruitt's security detail.
President Donald Trump tweeted last weekend that Pruitt has received "death threats" that justify his increased security spending.
White House press secretary Sarah Sanders was also asked Monday about the nature of the threats and said there was a "much larger number of security issues" surrounding Pruitt than previous administrators. The White House has initiated a formal review into issues surrounding Pruitt since reports that he rented a room in a Capitol Hill townhouse connected to lobbyists in his first six months in Washington.
Barrasso said in a statement Monday that he is waiting for the outcome of the White House review.
ABC News' Trish Turner contributed to this report.