On a conference call with agriculture reporters Tuesday Grassley said Pruitt had better follow through with ethanol mandates or "I'm going to be calling for Pruitt to resign because I'm done playing around with this".
"EPA's Protective Service Detail handles security decisions and this particular decision was made before Administrator Pruitt arrived at EPA", agency spokesman Jahan Wilcox said in an email.
Udall accused Pruitt of continuing to flout legal requirements to inform lawmakers about that and other big-ticket spending, and "treating your position of public trust as a golden ticket for extravagant travel and fine dining".
There has been no slowdown in damaging headlines for Pruitt since then, including revelations from the EPA's inspector general this week that Pruitt requested and received 24-hour security beginning his first day in office.
A House committee, the EPA's inspector general and the GAO all are investigating various allegations against Pruitt or his administration at EPA.
Pruitt repeated the claim that the extraordinary spending on his personal security was needed because the threats against him have been "unprecedented in terms of quantity and type".
On Wednesday, Pruitt repeatedly dodged directly answering whether he requested the stepped-up security coverage, saying career EPA officials below him made the final decision.
The new investigation brings the number of federal probes into Pruitt's conduct - related to his first-class travel, use of around-the-clock security, raises for his closest aides and the cheap housing he got from an energy lobbyist - to 12.
Despite the mounting investigations into Pruitt's actions, President Donald Trump has said he still supports his EPA chief.
Several Democrats on the subcommittee, including Senator Diane Feinstein and Senator Patrick Leahy, have called for Pruitt's resignation.