The Federal Reserve has not yet determined whether it would beable to legally implement negative interest rates in the U.S.,Chair Janet Yellen said.

“I would say that remains a question that we still would need toinvestigate more thoroughly,” Yellen said Wednesday in response toquestions from the House Financial Services Committee inWashington. “I am not aware of anything that would prevent us fromdoing it, but I'm saying we have not fully investigated the legalissues — that still needs to be done.”

A 2010 staff memo posted on the central bank's website late lastmonth cast doubt on whether the law that authorized the Fed to payinterest on excess reserves, or IOER, also would grant it theauthority to charge interest.