Former Pruitt aide to talk to congressional investigators this week

Kevin Chmielewski was deputy chief of staff for operations at EPA until he was placed on unpaid administrative leave. He had raised concerns within the agency about Administrator Scott Pruitt's spending and was then stripped of his work ID card and phone.

The sidelining of Chmielewski is similar to the way other EPA officials, including career employees and political appointees, have been pushed aside after raising concerns about Pruitt's practices or use of agency resources and funds.

The EPA did not immediately respond to a request for comment.

When CNN first reported on Chmielewski's suspension, EPA spokesman Jahan Wilcox said he is among "a group of disgruntled employees who have either been dismissed or reassigned." The agency has also defended Pruitt's spending, including his first class flights, frequent trips home, and his below-market rate rental of a Capitol Hill condo from a lobbyist.

Chmielewski was a senior aide on the Trump campaign responsible for setting up rallies and campaign events.

Then-candidate Donald Trump once invited him onstage and praised him as a "champ."

"He's tough as hell," Trump said. "Whenever there is a problem, he runs right in like full blast, runs in, he is a wild man."