Finance chairman meets with embattled acting IRS chief

Miller's visit to Capitol Hill also comes amid increasing questions about the acting commissioner's job security.

The acting commissioner and Doug Shulman, the former IRS chief, both found out about the extra attention given to conservative groups seeking tax-exempt status in May 2012, but did not inform lawmakers.

Miller is scheduled to testify on Friday at the House Ways and Means Committee, along with Russell George, whose office – the Treasury inspector general for tax administration – authored the audit. 

Baucus has vowed a thorough investigation of his own, while Attorney General Eric HolderEric H. HolderOvernight Tech: Senate moving to kill FCC's internet privacy rules | Bill Gates pushes for foreign aid | Verizon, AT&T pull Google ads | Q&A with IBM's VP for cyber threat intel Uber leadership sticking by CEO Top Dems prep for future while out of the spotlight MORE announced a Justice Department probe on Tuesday as well.

"The senator intends to get to the bottom of what happened here and expects to learn more as the committee conducts its investigation," Neary said. "He told Mr. Miller today that the committee will not accept anything less than his complete cooperation and transparency.”