WASHINGTON (CNN/Money) - A Republican lawmaker is asking the Securities and Exchange Commission to investigate former Treasury Secretary Robert Rubin's request last year that the Bush administration intervene to help now-bankrupt Enron Corp.

In a letter obtained by CNNfn, Florida Congressman Mark Foley asks SEC Chairman Harvey Pitt for an investigation of Rubin, now a high-ranking official with Citigroup.

It's been known that Rubin, who served through most of the two-term Clinton administration, put in a call to the current treasury undersecretary for domestic finance, Peter Fisher, on Nov. 8, 2001.

The purpose of the call was to ask for help to reassure nervous lenders about Enron's financial credibility. Fisher is on record as saying that he decided to do nothing in response to Rubin's call.

In the letter dated Thursday, Foley tells Pitt, "Apart from the questionable propriety of a former treasury secretary trying to solicit financial favors from former colleagues at a department he once led, I would ask that you investigate all [Enron stock] trades submitted by Citigroup and/or its subsidiaries and their clients in the two weeks preceding Mr. Rubin's call to Mr. Fisher, as well as the two weeks following the call."

Foley's letter notes, "Credit reports are viewed by investors in order to determine the financial soundness of a company before investing capital in that company's equity stock. ...It is imperative that we know what the consequences were on stock actions by Mr. Rubin's apparent attempt at interfering on behalf of Enron -- a company that Citigroup had, and has, a financial interest in."

Rubin joined Citigroup in 1999, a few months after he stepped down as treasury secretary near the end of the Clinton presidency. A company Web site lists Rubin as a director, chairman of the executive committee, a member of the Office of the Chairman of Citigroup Inc., and a member of the Citigroup Management Committee.

Leah Johnson, spokeswoman at Citigroup, denied that Rubin did anything improper.

"Bob Rubin had no knowledge or involvement in the Enron-related transactions," she said. And the phone call Rubin made last year was simply to ask Fisher to consider the merrits of asking the rating agencies to consider delaying their downgrades, she said.

"The issues that Representative Foley seems to be raising are untrue, and the suggestion is baseless," Johnson added.