WASHINGTON—Sen. Bernie Sanders (I., Vt.) has a slew of questions for Federal Reserve Chairman Ben Bernanke in the wake of new emergency-lending data the central bank released last week.

In a letter Monday to Mr. Bernanke, the senator who played a leading role in getting the Fed to unveil the loan data is demanding access to more information—including certain Fed officials' emails and phone logs as well as new details on the securities banks pledged in exchange for cheap loans.

Mr. Sanders asked about potential conflicts of interest between bank executives and Fed officials, and he asked the Fed to explain its rationale for lending to foreign banks.

He also wants to know exactly how much money the Fed lent to millionaires and billionaires during the financial crisis. He specifically asked for information on loans given to businessman H. Wayne Huizenga, billionaire hedge-fund manager John Paulson, Dell Inc. founder Michael Dell and Christy Mack, the wife of former Morgan Stanley chief executive John Mack and dozens of other borrowers.

"The emergency response appears to any objective observer to have been a clear case of socialism for the rich, and rugged free-market capitalism for everyone else," the Vermont Independent wrote. "Much of the information that you have provided on your website raises bigger questions than it answers, and some of the information mandated by the law appears to be missing."