Romney surrogate and former New Hampshire Gov. John H. Sununu (R) blasted the former Speaker on CNN's "Starting Point with Soledad O'Brien" Friday, saying he has a "serious problem."
"What do you think you're going to find in his [Romney's] taxes? The important thing is to find things that could be an October surprise problem," Sununu said. "Newt Gingrich has a serious problem with the package that the Ethics committee had when they fined him $300,000."
"Ring out the laundry. That's more important than anything else. Nancy Pelosi was on that group. If Nancy Pelosi knows, President Obama knows. We ought to be able to know now," he added.
Romney has been facing attacks form his GOP presidential rivals for not releasing his tax returns, with Gingrich saying that if there is a problem, voters should find out about it before a November matchup against Obama. The Romney camp responded Friday by calling on Gingrich to disclose more details of his House Ethics probe.
Gingrich was investigated for tax irregularities and for campaign finance disclosure violations in the late 1990s.
The matter, conducted when Republicans controlled the House, was settled when Gingrich paid a $300,000 fine for violating House rules.
On Thursday, Sununu conducted a conference call with reporters and said Gingrich should release "the complete records of the Ethics process."
"There still is a very important piece of opaque material out there on former Speaker Gingrich and that’s the record of what is in the Ethics process that he had done and taken," Sununu said on the call.
He said the Ethics probe could provide Democrats with an "October surprise" and that the lack of transparency made Gingrich a "vulnerable candidate."
House Minority Leader Nancy Pelosi (D-Calif.) last December threatened to unveil information about the Ethics probe of Gingrich.
“One of these days we’ll have a conversation about Newt Gingrich,” Pelosi said in an interview with Talking Points Memo.
“I know a lot about him. I served on the investigative committee that investigated him, four of us locked in a room in an undisclosed location for a year. A thousand pages of his stuff," she said.
Gingrich responded that Pelosi would be in violation of House Ethics rules if she disclosed information from the probe.
Gingrich and Romney are locked in a close battle in Saturday's South Carolina primary. Recent polls show Gingrich overtaking Romney after a series of strong debate performances.