Republicans want heads to roll in the wake of revelations that the Internal Revenue Service inappropriately targeted conservative groups for further scrutiny, and Florida Sen. Marco Rubio is asking Treasury Secretary Jack Lew to begin with the current IRS Commissioner.

“It is clear the IRS cannot operate with even a shred of the American people’s confidence under the current leadership,” Rubio wrote in a letter sent to Lew Monday. “Therefore, I strongly urge that you and President Obama demand the IRS Commissioner’s resignation, effectively immediately. No government agency that has behaved in such a manner can possibly instill any faith and respect from the American public.”

Rubio called the IRS’s actions “outrageous and seriously concerning,” and a “direct assault on our Constitution.”

House Oversight Committee Chair Darrell Issa vowed Friday that his committee would hold hearings and investigate the issue, and Rubio said that Lew and other high ranking Treasury and IRS officials should testify.

“The American people deserve answers about how such seemingly unconstitutional and potentially criminal behavior could occur, and who else was aware of it throughout the Administration. It is imperative that you, your predecessor, and other past and present high-ranking officials at the Department of Treasury and IRS immediately testify before Congress,” he wrote.

“The public expects your complete cooperation with both congressional investigations and potential criminal inquiries. If investigations reveal that bureaucrats or political appointees engaged in unconstitutional or criminal targeting of conservative taxpayers, they must be prosecuted to the fullest extent of the law. At a bare minimum, those involved with this deeply offensive use of government power have committed a violation of the public trust that has already had a profoundly chilling effect on free speech. Such behavior cannot be excused with a simple apology,” he added.

The IRS is currently led by Acting Commissioner Steven T. Miller. He assumed the role after IRS Commissioner Doug Shulman stepped down on November 9, 2012, but Rubio’s office notes that Miller was Deputy Commissioner during the time that the IRS was inappropriately scrutinizing conservative groups.

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