Two Republican congressmen are calling for a probe into alleged sweetheart deals by a controversial mortgage lender, after ties by a former Barack Obama aide to Countrywide Financial Corp. sparked questions about other arrangements with some members of Congress.

Reps. Darrell Issa of California and Mark Souder of Indiana called for the investigation in a letter to Rep. Henry Waxman, chairman of the House Oversight and Government Reform Committee. They said a probe is needed to make sure "tainted" officials recuse themselves from weighing in on legislation favorable to mortgage lenders.

The letter came after two senators, Chris Dodd, D-Conn., and Kent Conrad, D-N.D., were singled out as benefiting from low-rate loans from Countrywide. The lender has been criticized by Obama and others for contributing to the sub-prime mortgage meltdown. The company attracted new scrutiny nearly two weeks ago when it was reported that Jim Johnson, an adviser vetting Barack Obama's running mates, appeared to receive special treatment from Countrywide.

Johnson quit the campaign in response.

With charges that Dodd, Conrad and other former federal officials also benefited from a so-called VIP loan program, the two lawmakers are calling for a broader look into the lender's practices.

"With an allegation that the chairman of the Senate Committee managing legislation to bailout the mortgage industry may have received an improper benefit, Congress' investigative committee needs to ask questions about this alleged ‘VIP' program - including the question of who else may have benefited," Issa said.

Dodd is chairman of the Senate Banking Committee, and Conrad is chairman of the Senate Budget Committee.

"The VIP programs that may have given preferential treatment to government officials deserve to be investigated with the same zeal as was the link of executive pay to the mortgage crisis," Issa and Souder wrote in the letter to Wazman. "Additionally, we ask that you use your influence as chairman to stop any legislation bailing out mortgage lenders until all tainted individuals have recused themselves and the legislation has been examined and declared free of any undue influence."

Meanwhile, a conservative group led by former House Republican Leader Dick Armey is calling on Dodd to resign his chairmanship.

The group, FreedomWorks, sent an intern dressed in a panda suit -- as in "panda-monium" -- to Capitol Hill Wednesday to draw attention to its demand. The intern held an oversized novelty check for $75,000 made out to Dodd from Countrywide.

Armey also complained in a Wall Street Journal column Wednesday that the "scandal" should serve as a "political wake-up call" and warned about legislation Dodd and other senators are pushing that he said would "bail out the worst actors in the subprime mortgage banking industry."

A second group, Citizens for Responsibility and Ethics in Washington, filed a complaint against Conrad with the Senate ethics committee. Conrad has since donated the money he saved on the Countrywide loan to charity. He said he welcomes an ethics panel probe.

A spokesman for Conrad said the ethics committee has not started a formal investigation, but is in a preliminary process of determining whether a full inquiry is needed. He said Conrad has not talked to anyone from the committee.

Dodd, meanwhile, denied any attempt Tuesday to seek preferential treatment in the refinancing of two mortgages while acknowledging that he was a VIP customer. But he said he didn’t think that meant he would get special treatment.

The VIP program was reportedly known as "Friends of Angelo" -- or associates of Countrywide CEO Angelo Mozilo.

Dodd said he is not personally connected to Mozilo.

“There was no red flag to me that we were getting special treatment,” he said. “If anyone said to me ‘you were getting special treatment’ I would have rejected it.

Dodd said he “just thought it was a courtesy” because he had more than one mortgage, not because he is a U.S. senator.

FOX News' Chad Pergram, Trish Turner and Nicole Jackson contributed to this report.