NEW YORK (CNN/Money) - A member of the Senate panel investigating Enron's collapse called for Citigroup Chairman Sanford Weill and board member Robert Rubin to testify about what they knew of the company's finances, according to a letter disclosed Wednesday.

In a letter dated July 29, Sen. Peter Fitzgerald (R-Ill.), a member of the Senate Governmental Affairs Committee, asked committee Chairman Sen. Joe Lieberman (D.-Conn.) to invite Robert Rubin and Sanford Weill to testify.

Previous press reports have said that Rubin, the former Treasury secretary, called the Treasury Department in February representing Citigroup and seeking the Bush administration's intervention with credit rating agencies on Enron's behalf.

"I share your commitment to conducting a thorough investigation of what, until recently, was the largest bankruptcy filing in our nation's history," Fitzgerald said in the letter. "In light of recent news reports and testimony at this week's Permanent Subcommittee on Investigations hearing on the role of financial institutions in the collapse of Enron Corporation, I believe these two individuals could provide the committee with information critical to our investigation."

On Monday, Weill said in an affidavit to congressional investigators that he had no personal knowledge of an offshore entity dubbed Delta Energy Corp. that was established in 1993 by Citibank, five years before the bank merged with Weill's Travelers Group to form Citigroup Inc. (C: Research, Estimates).

Delta is central to investigators' probe into Citigroup's ties to Enron and its alleged role in the energy trader's collapse and bankruptcy.

The Senate's Permanent Subcommittee on Investigations on July 25 sent letters to Weill and J.P. Morgan Chase & Co. Inc. (JPM: Research, Estimates) CEO William Harrison about the banks' use of shell offshore firms allegedly to aid Enron's deceptive accounting.

Enron Corp. went bankrupt in December after allegedly using a shadowy web of offshore balance sheet transactions to hide massive debts and inflate profits.

Congressional investigators have accused Citigroup and J.P. Morgan of providing Enron with $8.5 billion in loans disguised as commodity trades conducted through offshore shell companies, including Delta Energy.