WASHINGTON—Sen. Robert Menendez of New Jersey urged the Federal Reserve last July to approve an acquisition to save a struggling bank in his state. He didn't mention that the bank's chairman and vice chairman were big contributors to his political campaign.

If the acquisition had been approved, it would have prevented the two executives from losing what was left of their investments in the bank.

In his letter to the Fed July 21, Mr. Menendez said there was a strong likelihood that First BankAmericano, of Elizabeth, N.J., would fail in three days, which would "send yet another negative message to consumers and investors and further impact our fragile economy." The one-page letter, obtained by The Wall Street Journal under the Freedom of Information Act, urged Fed Chairman Ben Bernanke to approve a sale of the bank to JJR Bank Holding Co. of Brick, N.J.

The Fed didn't act on the request from Mr. Menendez, a Democrat, and First BankAmericano, which was closely held, failed July 31.

While lawmakers routinely forward requests from constituents to government agencies, it is rare for them to make specific requests along the lines of this letter asking specific actions, bank attorneys and congressional aides said. One reason is to avoid any appearance of trying to influence the regulatory process for political ends.