Mitt Romney requested at least 10 years of tax returns from several of his potential running mates during the vice presidential vetting process, three Republicans familiar with the requests confirmed to CNN.
One GOP source said that while Romney officials asked for a decade's worth of tax documents, they were "were willing to settle for less" as they scrutinized the financial backgrounds of several Republicans before Romney ultimately decided to tap Wisconsin Rep. Paul Ryan as his ticket mate.
The fresh details about the tax requests, first reported Thursday by The Daily Beast, threaten to complicate Romney's message as he continues to reject calls from President Barack Obama's campaign team to release more than just two years of his own tax returns.
Democrats say Romney, who accumulated a substantial fortune during a nearly two-decade career in consulting and private equity, needs to show voters what tax rate he paid and provide more details on financial assets held in offshore bank accounts.
Romney faced similar pressure from his Republican primary opponents last winter.
Citing privacy, the former Massachusetts governor has promised to release two years of his tax returns, but no more. He has made his 2010 return public and says he will release his full 2011 tax filings before Election Day.
Romney paid an effective tax rate of 13.9 percent in 2010.
"The Obama people keep on wanting more and more and more: More things to pick through, more things for their opposition research to try to take a mountain out of and to distort and to be dishonest about," Romney told Fox News in July, noting that "none of the tax returns are required by law to be put out."
But Ryan, in an interview with "60 Minutes" after his selection in August, said that he was asked to submit "several" years of tax returns to the Romney campaign during the vetting process. He declined to say exactly how many years.
He called the tax questions a distraction and said he planned to follow Romney's lead and release two years of returns -- the same number that GOP nominee John McCain made public in 2008.
Another Republican vetted for the vice presidential job, former Minnesota Gov. Tim Pawlenty, also said he submitted "several years" of tax documents but would not say how many. Romney's point person on the vice presidential search, his longtime adviser Beth Myers, said the same.
The Obama campaign released a new Web video Friday seizing on the transparency issue and accusing Romney of "ducking and dodging on his tax returns."
"That's one set of rules for Romney and another set for everyone else," a narrator says in the video, which highlights the 10 years of tax returns requested by the Romney campaign during the vetting process.
The Romney campaign, which has steadfastly avoided discussing the vice presidential search process, did not respond to a request for comment.