Washington (CNN) Environmental Protection Agency Administrator Scott Pruitt routinely directed staffers to book expensive hotels, help him earn frequent flier miles and schedule meetings to align with his personal travel desires, a former top staffer told congressional investigators.

Former EPA deputy chief of staff, Kevin Chmielewski also said Pruitt was aware of major raises given to other aides, rebutting Pruitt's account that he was unaware of the salary bumps.

The allegations are laid out in a letter several Democratic members of Congress sent Pruitt and President Donald Trump on Thursday. The letter says the new information about how Pruitt has run the agency reveal actions that are "unethical and potentially illegal."

Chmielewski is currently on unpaid leave from the agency after raising concerns about Pruitt's travel practices and uses of resources and funds.

Among the allegations:

• Pruitt declined to use State Department-approved overseas hotels that already had security in place, preferring more expensive hotels with higher security costs.

• Pruitt requested aides to schedule official business in cities he wanted to visit.

• Pruitt directed staffers booking his travel on Delta to maximize his personal frequent flyer miles.

• Pruitt used the agency's scheduling director as a "personal real estate representative."

• Pruitt wanted staff to find reasons for him to visit his home state of Oklahoma.

• Pruitt spent more than the $5,000 allowed by law to decorate his office, including refinishing an antique desk, buying a standing desk and paying leases for art on loan from the Smithsonian.

"We will respond to Members of Congress through the proper channel," the agency's spokesman, Jahan Wilcox, told CNN in a statement.

The EPA has previously defended Pruitt's travel and security practices, and Pruitt argued in recent interviews his lease was ethically sound. EPA has also said Chmielewski is among "a group of disgruntled employees who have either been dismissed or reassigned."

Chmielewski confirmed in a brief phone interview that the letter from Democratic members of Congress laying out his closed-door testimony is accurate. He has met with both Democratic and Republican members of Congress as part of inquiries into Pruitt.

"This has nothing to do with Republicans or Democrats. This is right and wrong. I will meet with whoever wants to meet with me," Chmielewski told CNN.

Hotel choices

The letter reveals that when Pruitt was planning a business trip last year to Australia, he ignored State Department recommendations.

"Mr. Chmielewski claimed that you refused to stay at hotels recommended by the U.S. Embassy, although the recommended hotel had law enforcement and other U.S. resources on-site," the letter reads. "He alleged you chose to stay instead at more expensive hotels with fewer standard security resources, and to bring your security team with you, at taxpayer expense."

Pruitt's hotel choices have also required his security detail to pay for rooms out of their own pockets.

"According to Mr. Chmielewski, you frequently stayed in hotels that exceeded the allowable U.S. government per diem," the letter said. "He added that while you were reimbursed for these expenses, on some occasions members of you security detail were not reimbursed for the portion of their expenses that exceeded allowable maximums."

First class travel and pay raises

Chmielewski told investigators he was sidelined at Pruitt's direction after refusing to retroactively approve a first-class plane ticket for another EPA political appointee, Samantha Dravis. Dravis announced last week that she is leaving the agency later this month.

"He told our staffs that following his refusal, chief of staff Ryan Jackson called Mr. Chmielewski into his office and informed him that you wished to fire or reassign him," the Democratic members of Congress wrote to Pruitt.

Chmielewski told congressional investigators that he had personal knowledge -- through a conversation with Jackson -- that Pruitt was involved in the raises given to his agency attorney and the scheduling director.

Pruitt denied in a Fox News interview that he knew of the raises prior to a report by The Atlantic that uncovered the raises -- one for $57,000 and another for $28,000.

But Chmielewski said the administrator was in the know.

"Mr. Chmielewski explained that he was called into your Chief of Staff's office and told that you wanted to move him out of his position in order to give Ms. Hupp his title and a pay increase," the letter to Pruitt reads.

The raises were "100% Pruitt himself," Chmielewski told the investigators. The letter did not specify if Chmielewski has personally discussed the raises with Pruitt.