Washington (CNN) -- Congressional Democrats revealed new documents on Friday indicating the Internal Revenue Service subjected both liberal and conservative organizations to additional tax scrutiny in recent years, raising new questions about assertions of unfair politically based targeting.
Maryland Rep. Elijah Cummings, the top Democrat on the House committee investigating the matter, asked his GOP counterpart to summon the Treasury Department's chief investigator, J. Russell George, to a panel hearing scheduled for next Thursday.
"Given the new documents obtained by the committee ... I believe it is necessary to call (George) back before the committee to explain why he failed to disclose this critical information," Cummings wrote in a letter to California Rep. Darrell Issa, the chairman of the House Oversight and Government Reform Committee.
Cummings blasted the behavior of George and Issa, arguing that the IRS probe "has been characterized by one-sided and partial information leading to unsubstantiated accusations with no basis in fact."
Issa and other Republicans have insisted for months that after President Barack Obama was first elected, the IRS started unfairly targeting conservative outfits seeking tax-exempt status.
Cummings and his fellow Democrats argue the IRS improperly scrutinized groups on both the left and right as part of a clumsy attempt to administer vague election-related tax laws.
Among other things, Cummings on Friday released slides from a July 2010 workshop PowerPoint presentation instructing IRS agents to watch for organizations with names like "Tea Party," "Patriots," "9/12 Project," and "Progressive."
One of the slides shows a picture of an elephant and a donkey -- the symbols of the Republican and Democratic parties.
Another slide notes a concern that the activities of such groups "may be more than 50% political," thereby ruling out the possibility of tax-exempt status under current law.
Notes from the workshop indicated that "if in doubt," IRS staff should "err on the side of caution" and transfer cases to "7822," the IRS office in Cincinnati responsible for reviewing applications for tax-exempt status.
The word "progressive" was again cited as an organization name that should trigger a review.
Cummings also revealed a May 2013 e-mail from George's deputy noting that 5,500 internal IRS e-mails were reviewed as part of an effort to discover any directing of staff to target "Tea Party and other political organizations," as well as any subsequent coverup.
"There was a Be On the Lookout (BOLO) list specifically naming these groups," the deputy inspector general's e-mail notes. "However, the e-mails indicated the organizations needed to be pulled because the IRS employees were not sure how to process them, not because they wanted to stall or hinder the application."
The deputy's e-mail goes on to stress that "there was no indication that pulling these selected applications was politically motivated."
In his letter to Issa, Cummings said, "It is unclear why Mr. George failed to disclose this significant information to Congress."
A report released by George's office in May indicated that lax oversight at the IRS allowed for the singling out of some conservative groups. George subsequently testified that he could not specifically identify whether any liberal groups were similarly targeted.
"This new information underscores the fact that the Treasury inspector general's audit was fundamentally flawed and created widespread misperceptions that Republicans seized on in an effort to attack the White House," said Michigan Rep. Sander Levin, another top House Democrat.
"It is now all the more important that Inspector General George return to Congress to explain his glaring omissions and reasons for releasing a highly misleading report."
A spokesman for Issa, however, drew a different conclusion, highlighting the fact that the workshop minutes noted that an IRS "Tea Party Coordinator/Reviewer" said that 'Progressive' applications are not considered 'Tea Parties.'"
"These documents, once again, refute misleading attempts to equate routine scrutiny of other groups involved in advocacy to the systematic scrutiny of Tea Party groups by IRS officials," spokesman Ali Ahmed told CNN.
"As has been documented, while 100% of Tea Party applications were systematically stopped and scrutinized for a 27-month period, at the same time dozens of progressive applications were approved by the IRS," Ahmed said, referencing a June 26 letter from George to Levin.
In a statement released Wednesday, Issa said, "IRS officials have told committee investigators that they understood Tea Party applications were being isolated from other cases and subjected to extra scrutiny to ensure fair, efficient, and consistent treatment."
"The evidence gathered in this investigation makes clear that had Washington IRS officials simply kept their hands off these cases and allowed employees in the Cincinnati office to process applications independently, instead of facing excessive delays, these cases would have been processed just like other advocacy cases," he concluded.