Miller's visit to Capitol Hill also comes amid increasing questions about the acting commissioner's job security.
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. HolderEllison needles Perez for 'unverifiable' claim of DNC support With party in trouble, Dems hit voting laws Bottom Line 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.”