(CNN) -- The admitted targeting of conservative groups applying for tax exempt status by the Internal Revenue Service prompted more calls for tough consequences and a congressional investigation Monday.
Even Democrats voiced concern at the IRS' actions, including Sen. Max Baucus, the chairman of the Senate Finance Committee.
"These actions by the IRS are an outrageous abuse of power and a breach of the public's trust. Targeting groups based on their political views is not only inappropriate but it is intolerable," Baucus wrote in a statement, adding the agency "should be prepared for a full investigation into this matter" by his Senate panel.
Sen. Marco Rubio, R-Florida, demanded the resignation of the IRS commissioner in a letter the Treasury Secretary Jack Lew on Monday, noting the agency "cannot operate with even a shred of the American people's confidence under the current leadership."
"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," he continued, adding that a mere apology wouldn't go far enough regaining the American people's trust.
The current acting commissioner of the IRS is Steven Miller, who assumed the role in November 2012. The previous commissioner, Douglas Shulman, was appointed by President George W. Bush. Shulman testified at a March 2012 congressional hearing that his agency did not target conservative groups for political reasons.
Keli Carender, a national coordinator for the Tea Party Patriots, listed a spate of questions for the tax agency and President Barack Obama during an appearance on CNN's "Starting Point."
"We need to know how did this start? Who started it? Who knew what? And when did they know it? How far up does this go? Does it go up all the way into Treasury? Does it go up into the administration? Who is a part of this? How are these decisions made? And, and what is going to happen to the people that did it?"
Her list has been echoed by Republicans and activists in light of the IRS' admission on Friday they used the words "tea party" and "patriot" to screen tax-exempt applications, applying extra scrutiny to those groups that included requests for pages upon pages of documentation.
A congressional investigation would probe who knew what and when, Rep. Darrell Issa told CNN Sunday. Issa is the chairman of the House Committee on Oversight.
"The fact is if you're doing something and it's wrong, it's illegal, it's the kind of thing that scares the American people to their core, when Americans are being targeted for audits based on their political beliefs, that needs to change," he said.
Sen. Carl Levin, the Democratic chairman of the Senate committee responsible for investigations, said on Friday the IRS actions require a government probe.
The IRS says there was no political motivation in their scheme, which was established after a flood of applications for 501(c)4 status after the Supreme Court's Citizens United ruling in 2010.
But Republicans say any bias toward groups based on their political ideology is an unacceptable breach of the public trust.
"It contributes to the profound distrust that the American people have in government. It is absolutely chilling that the IRS was singling out conservative groups for extra review," Sen. Susan Collins, R-Maine, said on Sunday's "State on the Union" on CNN.
She and other Republicans are calling for a public condemnation of the IRS' actions by President Barack Obama, who has yet to speak publically about the agency's admission.
"I think that it's very disappointing that the president hasn't personally condemned this and spoken out," Collins told CNN chief political correspondent Candy Crowley.
Obama spokesman Jay Carney said Saturday the president believes the government should be staffed with "the very best public servants with the highest levels of integrity" and that "based on recent media reports, (the president) is concerned that the conduct of a small number of Internal Revenue Service employees may have fallen short of that standard."
Rep. Mike Rogers, who chairs the House Intelligence Committee, called for a full investigation of the IRS' practices, something Republicans and Democrats have said is necessary after learning of the conservative targeting.
"I don't care if you're a conservative, a liberal, a Democrat or a Republican, this should send a chill up your spine," Rogers said on "Fox News Sunday."