Democrats in Congress have highlighted the possibility that liberal groups were also abused to counter charges by some Republicans that that the targeting was politically motivated.
Congressional investigations have so far shown that IRS supervisors in Washington including lawyers in the chief counsel's office oversaw the processing of tea party applications. But there has been no evidence that anyone outside the IRS directed the targeting or that agents were politically motivated.
"The facts are very clear not only were conservative groups targeted by the IRS, but they received much higher scrutiny than progressives," said Rep. Dave Camp, R-Mich., chairman of the Ways and Means Committee.
"However, this is just the tip of the iceberg," Camp said. "We have received less than 3 percent of the documents responsive to the investigation. So, Congress will continue to investigate how the targeting began, why it was allowed to continue for so long and what the IRS is doing to resolve this. Americans deserve to know the full truth."
The IRS said in a statement that 70 agency lawyers are working full-time to review documents for congressional inquiries.
"The IRS is aggressively responding to the numerous data requests we've received from Congress," IRS spokeswoman Michelle Eldridge said. "We are doing everything we can to fully cooperate with the committees, and we strongly disagree with any suggestions to the contrary."
A report by the IRS inspector general said the agency gave extra scrutiny to 298 groups when they applied for tax exempt status from the spring of 2010 to the spring of 2012.
A total of 104 applications included the labels "conservative," ''tea party," ''patriot" or "9-12" in their names, according to the Ways and Means report, which is consistent with the inspector general's report. Seven included the words "progressive" or "progress."
While processing the applications, IRS agents asked the progressive groups an average of 4.7 questions and eventually approved all seven applications, according to the analysis by Ways and Means Republicans. Some progressive groups, however, complained about lengthy delays.
The conservative groups were asked an average of 14.9 questions and, as of May 31, only 48 applications had been approved. The other 56 applications were either pending or withdrawn. None was denied.
Rep. Sander Levin of Michigan, the top Democrat on the Ways and Means Committee, said the analysis omits other liberal or progressive groups that don't have the word "progressive" in their names.
"This is a recurring problem in this investigation the release of incomplete information," Levin said. "Indeed, that is exactly what led to fundamental flaws in the (inspector general's) report."
During the 2010 and 2012 elections, IRS agents singled out groups that had "tea party," ''patriots," and "9-12" in their applications, according to a May report by IRS inspector general J. Russell George. George's report determined that these groups received extra, sometimes burdensome scrutiny that delayed their applications for more than a year.
George's report did not mention progressive groups. He told a congressional committee this month that, despite a yearlong inquiry, the IRS just recently provided him documents suggesting that progressive groups may have been targeted.
The IRS was screening the groups' applications because agents were trying to determine their level of political activity. IRS regulations say tax-exempt social welfare organizations may engage in some political activity, but the activity may not be their primary mission. It is up to the IRS to make that determination.
"The inspector general just testified that his audit was based on an incomplete set of documents that was missing key information about progressive groups, and now House Republicans are making the same mistake," said Rep. Elijah Cummings of Maryland, the top Democrat on the House oversight committee. "Rather than conducting a responsible investigation to determine all of the facts, Republicans are desperate to continue making completely unsubstantiated accusations of political motivation."
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