Merrill Lynch, the wealth manager owned by Bank of America, has been fined $2.8 million for supervisory failures that led to it overcharging clients $32 million in unwarranted fees.

The US Financial Industry Regulatory Authority also imposed the fine on the US securities firm for failing to provide certain required trade notices.

Merrill Lynch has repaid the nearly 100,000 affected clients with interest.

Brad Bennett, FINRA's chief of enforcement, said that investor confidence is threatened if investors are not able to trust that the fees charged by securities firms are correct.

The regulator found that Merrill Lynch failed to have an adequate supervisory system to ensure that customers in certain investment advisory programs were billed in accordance with contract and disclosure documents between April 2003 and December 2011.

FINRA said in a statement that Merrill Lynch consented to its findings but neither admitted nor denied the charges.

Last month, the regulator flexed its muscles against the banking giants when it fined Wells Fargo, Citigroup, Morgan Stanley and UBS around $7.3 million plus $1.8 million in restitution collectively, over sales of certain exchange-traded funds.