Congressional disgust with IRS Commissioner John Koskinen deepened on Wednesday after his claim that the agency effectively encourages illegal immigrants to file tax returns using fraudulent Social Security numbers, with lawmakers calling for his ouster.

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"I think it certainly is appropriate to talk about new leadership," South Carolina Sen. Tim Scott, a Republican who sits on the Senate Finance Committee, told the Washington Examiner.

Koskinen on Tuesday told Scott's committee that the agency does not take action when tax returns are submitted using fraudulent personal information. "It's not the normal identity theft situation," Koskinen said, adding that it helps the government to collect more revenue.

Members continued to press Koskinen on the issue on Wednesday when he testified before a panel of the House Small Business Committee. "If folks are here illegally, I get that you want to collect tax revenue ... but should any agency go along with what it knows to be illegal activity?" asked Virginia Republican Rep. Dave Brat.

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Koskinen held firm, saying his agency's main goal is to maximize revenue, not to enforce the law. "The tax code is set up, and our obligation, everybody who is earning money has an obligation to pay taxes, and we do everything we can to make sure they pay those taxes," he said. "To the extent that to get the employment, they've borrowed or somehow gotten a Social Security number, that's not a jurisdiction we have.

"Our job is to make sure people pay the taxes they owe from the earnings they've had," he added. "To the extent that they're here under circumstances that don't meet the immigration laws or don't correspond with the Social Security Administration, it's really [other] agencies' job to pursue that."

Yet whether Koskinen's interest is genuinely in optimizing revenue, experts pointed out, is impossible to judge based on facts, because the IRS does not disclose the data. "In one sense, he was not telling the truth when he said their only interest is in maximizing revenue," said Mark Krikorian, executive director of the Center for Immigration Studies. "It's entirely plausible that the U.S. Treasury loses money when illegal immigrants file tax returns… The IRS has a way of knowing, but we don't."

Though Koskinen was appointed to renew trust in the IRS after it was discovered the agency had improperly targeted conservative groups under his predecessor, Lois Lerner, that has not happened to date. In fact, historic skepticism of the agency largely helped to fuel an October resolution in the House calling for his impeachment over "deception" and "destruction of evidence" related to the agency's improper targeting.

Though the bill has 62 cosponsors, it has largely languished since its introduction. After the newest admission, members were reminded that it was still on their agenda.

"Koskinen's comments were troubling, to say the least," said Texas Republican Rep. Louie Gohmert, one of the resolution's cosponsors. "This admission that the agency is complicit in rewarding illegal immigrants' use of stolen Social Security numbers displays the IRS' unaccountable, arbitrary, capricious nature," and further supports Koskinen's impeachment "for high crimes and misdemeanors," he said.

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"It's the alternate universe in which too many people in this administration live," Scott said. "It's hard to understand and digest Koskinen's answers to a number of questions. [They] should cause us all to pause and say 'What?' That really is your response to a question on the record?

"It's obvious that if he was brought in to be the 'fix it' man, things have gotten worse, not better," he said.