The investigation of that rental — from the wife of a lobbyist who had clients had business with the EPA — will be the fifth inquiry being conducted by the EPA's Office of Inspector General into questions related to Pruitt's tenure.
The OIG already was eyeing Pruitt's use of first-class flights for business travel, millions of dollars in spending on his security staff, approvals for big raises for a number of employees, and reassignment or demotions of certain staff.
The Government Accountability Office last week found that the EPA had violated federal spending rules by its approval of a $43,000 soundproof booth for Pruitt's office.
OIG's plan to now review Pruitt's rental, for just $50 per night, of a room in a condo on Capitol Hill was disclosed in a letter Inspector General Arthur Elkins Jr. sent to Rep. Ted Lieu, D-Calif.
Earlier this month, Lieu and Rep. Don Beyer, D-Va., had called for a probe of the rental, saying there is a concern it violated ethics rules.
Elkins' letter also mentions the other pending inquiries when it says OIG will be looking into "housing arrangements by the Administrator."
"We have received multiple requests from multiple members of Congress, as well as other OIG Hotline complaints, regarding these same and related issues," Elkins wrote.
A spokesman for Pruitt, when asked about the new probe, said, "We do not comment on matters pertaining to EPA's IG."
An EPA ethics official, Kevin Minoli, had initially ruled that Pruitt's rental of the room from Vicki Hart, wife of lobbyist Steven Hart, would not violate federal ethics rules. But Minoli later said he did not have sufficient information about the deal to determine if Pruitt honored the terms of the lease.
Pruitt testified for hours Thursday to two House committees. He said he has "nothing to hide" during that testimony, and that much of what has been reported about him is "half-truths or stories that have been so twisted that they do no resemble reality."
Pallone also said that if he were president, "I'd just get rid of you."
Lieu, in a statement issued Friday, said, "I am pleased the EPA OIG has honored the request I made with Rep. Beyer and others to review Administrator Scott Pruitt's purported misconduct."
"The Inspector General's letter also mentions new matters under review, which shows that Pruitt's alleged corruption may run deep. No one is above the law."
Lieu also tweeted about the probe, saying "My #FridayFeeling is that Scott Pruitt is in deep trouble."
Additional reporting by Ryan Ruggiero