The travel costs of the Environmental Protection Agency's chief came under fresh scrutiny this week after a watchdog group and The Washington Post revealed new details about the Trump appointee's penchant for first-class flights.

Administrator Scott Pruitt has previously come under fire for his pricey transportation bill, an issue that has already brought down one Trump deputy, former Health and Human Services Secretary Tom Price. At the request of Democrats, the EPA's inspector general is investigating the cost of Pruitt's travel — including several first-class trips to his home state of Oklahoma — and his security detail.

Now, records show taxpayers shelled out at least $90,000 during a stretch of January when Pruitt and aides flew from Washington to New York and to Cincinnati and Rome. The receipts were made public by the Environmental Integrity Project through a Freedom of Information Act request.

Pruitt's itinerary started with a $1,641 first-class flight from Washington to New York on June 5 to tout President Donald Trump's decision to pull the United States out of the Paris climate agreement in a pair of brief television interviews, the Post reported on Sunday evening. The cost of the ticket was more than six times the airfare paid for two media aides, who flew coach, according to the Post.

Two days later, at a cost to taxpayers of $36,068.50, Pruitt and several staffers hopped a military plane to New York from an event promoting Trump's infrastructure plan in Cincinnati, according to the records. In New York, the group caught a flight to Rome. The price of Pruitt's round-trip ticket was more than $7,000, several times the fare paid for other officials, the Post reports.

The EPA did not immediately return a request for comment from CNBC on Monday.

EPA spokeswoman Liz Bowman told the Post the travel expenses have been approved by federal ethics officials. She said the New York trip helped the administration communicate its message and Pruitt is "hearing directly from people affected by EPA's regulatory overreach" on other domestic trips.