After a tense exchange with Acting IRS Commissioner Danny Werfel Friday, House Oversight and Government Reform Committee Chairman Darrell Issa sent a subpoena to the Treasury Department Friday demanding more documents and accusing the agency’s chief counsel’s office of being “compromised.”

Issa, R-Calif., accused the Internal Revenue Service of dragging its feet in responding to the committee's demand for documents related to IRS targeting of conservative groups — a charge Werfel denied.

During an Oversight subcommittee hearing, an agitated Issa said the IRS is “slow-rolling us.”

“That’s not true,” Werfel countered.

But Issa persisted, saying he would go over Werfel's head and ask his boss, Treasury Secretary Jack Lew, to respond to his requests.

“I’ve asked you for information; you’re not forthcoming,” Issa told Werfel. “The office of chief counsel, a politically appointed office, has been compromised.”

“Our expectation is that Treasury Department will take over the delivery of documents in a timely fashion,” Issa said. He insisted that Werfel remove the IRS counsel’s office from any “decision making” related to the inquiry. The IRS is an agency within the Treasury Department.

Werfel remained steadfast in defending the agency’s record of responding to congressional inquiries.

“This is not about obstruction,” he said. “This is about offering as much information as we can.”

In fact, Werfel said, about 70 IRS attorneys are reviewing documents full time in an attempt to respond to seven congressional committee investigations.

“By any measure, this is an enormous undertaking for the IRS,” he said. “We are aggressively working to share, gather and provide information requested by your committee and others, and we continue to do so.”

Over the last two weeks, Issa has focused his investigation on the potential involvement of William Wilkins, the IRS chief counsel. Wilkins is one of two Obama-appointed positions at the agency. The testimony so far has shown that Wilkins’ office, with some 1,600 attorneys, was involved in the targeting.

Werfel argued that the agency has already provided six related documents and offered the committee a chance to interview Wilkins – an interview the staff said they would prefer not to do at this time.

The top Democrat and Republican on the Senate Finance Committee, which oversees tax matters, on Friday also expressed frustration with the IRS' slow response to requests for information.

Sens. Max Baucus, D-Mont., and Orrin Hatch, R-Utah, sent to the IRS in May a list of 41 questions regarding the inspector general report that detailed the IRS’ targeting of Tea party groups. So far, the senators said, the IRS has given incomplete answers to 13 of the questions and hasn’t even attempted to answer 10 others.

“The IRS needs to be more cooperative in providing us with the documents needed to fully carry out this investigation,” they said in a joint statement.