WASHINGTON — Scott Pruitt, the Environmental Protection Agency administrator, insisted on staying in luxury hotels that were costlier than allowed by government standards, while also pushing to fly on an airline not on the government’s approved list so he could accrue more frequent flier miles, one of his top former deputies at agency has told congressional investigators.

The new allegations are detailed in a scathing six-page letter signed by two senators and three House lawmakers — all Democrats — whose staff members met this week with Kevin Chmielewski, who served as the E.P.A.’s deputy chief of staff until he was removed from his post after raising objections to this and other spending.

In a separate letter on Thursday, Democratic lawmakers also demanded information about two previously unknown E.P.A. email addresses that have been used by Mr. Pruitt, asking if they were a tool for withholding public information from records requests. Their letter echoes a controversy in 2012, during the Obama administration, when Lisa P. Jackson, who was E.P.A. chief at the time, was criticized for a similar use of an undisclosed E.P.A. email account.

Jahan Wilcox, a spokesman for the E.P.A., said the agency had consistently searched all email addresses associated with Mr. Pruitt when responding to records requests. Of the allegations outlined to lawmakers by Mr. Chmielewski, he said, “We will respond to members of Congress through the proper channel.”