(CNN) - An independent fact-checking group, FactCheck.org, claimed Friday that a new Obama campaign ad attacking Mitt Romney over a tax avoidance scandal is "badly misleading."
"The Obama campaign strikes another low blow with a TV spot accusing Mitt Romney of 'personally' approving a notoriously abusive tax-avoidance scheme and suggesting he may have paid 'zero' tax," the FactCheck.org article states. "That's badly misleading."
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The spot, released Thursday by the president's re-election campaign, points to an op-ed by two tax experts who claim Romney was involved with the reporting of a $70 million fictional tax loss when he served on the board of Marriott International from 1993 to 1998.
"During that period, Marriott engaged in a series of complex and high-profile maneuvers, including 'Son of Boss,' a notoriously abusive prepackaged tax shelter that investment banks and accounting firms marketed to corporations such as Marriott," states the op-ed, which was published this week on CNN.com.
The authors –Peter C. Canellos, former chair of the New York State Bar Association Tax Section, and Edward D. Kleinbard, former chief of staff of Congress's Joint Committee on Taxation–wrote that the "Son of Boss" tax shelter marked "perhaps the largest tax avoidance scheme in history" and cost the U.S. "billions in lost corporate tax revenues."
While Romney did not face criminal charges, unlike others linked to the scandal, the authors wrote "his endorsement of this stratagem provides insight into Romney's professional ethics and attitude toward tax compliance obligations."
But FactCheck.org said Friday that Marriott wasn't the only company involved in the "Son of Boss" scheme.
"Viewers (of the ad) may get the mistaken impression that Romney – actually Marriott – is solely to blame for 'one of the largest tax avoidance schemes in history.' Not true. It was a strategy used by many taxpayers that resulted in billions in lost revenue," the article states.
The Obama ad also doesn't give context about Marriott, FactCheck said, and leads the viewer to believe it was Romney who personally handled the deal.
"The tax scheme didn't benefit Romney, and the fictional losses were not his," FactCheck says. "The company involved was Marriott Corp, not Romney or Bain Capital. But the ad gives no hint of this."
Furthermore, the website states that the term "tax avoidance" is technically legal, a distinction not easily communicated in the new spot.
"Combining 'avoidance' with loaded terms like 'scheme' and 'notorious' and 'scandal' and 'fictional losses' further suggests possible tax fraud, but there's no evidence Romney broke any law," the article states.
The spot comes at a time when top Democrats and Obama's campaign have actively worked to raise suspicion about Romney's tax history. They've unleashed a flood of calls urging the presumptive GOP nominee to release more tax returns as a way to answer questions about his financial portfolio.
The Republican candidate, whose estimated worth is valued up to $256 million, has made public his tax return for 2010 and an estimate for 2011, with a pledge to release the full year once the documents are complete. He filed an extension for October.
While Romney says he will not release further taxes than what he has already made public, a majority of Americans disagree with his decision. According to a CNN/ORC International poll released Thursday, 63% of Americans said Romney should release additional tax returns.