A spokeswoman for the Treasury Department had no comment on Geithner's memo.

Libor is used as a benchmark for an estimated $10 trillion in loans worldwide, including the interest paid by consumers on many variable-rate mortgages and credit cards in the United States.

It also is used as the basis for trading in an estimated $350 trillion in derivatives worldwide by major banks, so the manipulations may have cost pension funds and local governments that were trying to protect themselves against changes in interest rates by buying the derivatives.

The British Parliament has already held hearings into the Barclays' Libor scandal. But despite the request for documents by Neugebauer's House subcommittee, there have been no hearings held in the United States so far.

Rep. Peter Welch, a Vermont Democrat, is circulating a letter among members of Congress calling on Attorney General Eric Holder to "carefully investigate and aggressively prosecute all senior bank officials who participated in manipulating" Libor.

But the Justice Department already disclosed in February that it is conducting a criminal investigation into alleged manipulation of Libor. That disclosure came in a filing in a civil class action suit revolving around Libor manipulation.

-- CNNMoney reporter James O'Toole and CNN's Deirdre Walsh contributed to this report.