NEW YORK -- A financial regulator has fined Merrill Lynch $2.8 million for overcharging customers with fees and for failing to provide timely trade confirmations.

The Financial Industry Regulatory Authority said Thursday that it fined Merrill Lynch, Pierce, Fenner & Smith after it found the broker overcharged nearly 95,000 customer accounts with fees totaling more than $32 million from April 2003 to December 2011.

"Investors must be able to trust that the fees charged by their securities firm are, in fact, correct," said Brad Bennett, the regulator's chief of enforcement. "When this is not the case, investor confidence is threatened."

The agency said Merrill Lynch has since returned the overcharges, with interest, to affected customers.