Wall Street's industry-funded watchdog is weighing fresh enforcement cases against brokerage firms alleged to have overcharged mutual fund investors, an official with the Financial Industry Regulatory Authority said Tuesday.

The cases now under investigation by Finra are similar to one brought last year against Bank of America’s Merrill Lynch unit, which resulted in the firm paying an $8 million fine.

Finra's review involves overcharges paid by charities and retirement accounts that invested in funds sold by brokerages, said Bradley Bennett, Finra’s enforcement chief, at an event for compliance professionals in New York.

"I think you'll see some activity on that front," Bennett said.

The Merrill Lynch case prompted some firms to review their practices to see whether they, like Merrill, had failed to provide the sales charge discounts that mutual fund issuers had made available to retirement accounts and charities, Bennett told Reuters.

Those firms self-reported their concerns to FINRA. The firms would have to reimburse any unpaid discounts to customers, Bennett said.

Bennett did not identify the firms that self-reported their lapses or comment on the timing of future enforcement cases.

In the Merrill case, the firm had to reimburse customers $24.4 million, in addition to $64.8 million it had already repaid, making the total payout about $97.2 million including the fine.

Like many rivals, Merrill has offered mutual fund shares in multiple classes. Typically, Class A shares carry lower fees than Class B and C shares, but carry upfront sales charges.

Finra had said Merrill failed to provide promised sales charge waivers on many retirement accounts for more than five years beginning in January 2006, relying instead on financial advisers it did not properly supervise to do so.