Tokyo prosecutors plan to indict SMBC Nikko Securities Inc. for alleged market manipulation, according to the Nikkei newspaper, in what’s set to be a blow to one of Japan’s biggest brokerages and its second-largest megabank.

The prosecutors determined employees weren’t sufficiently supervised despite having conducted allegedly illegal trades repeatedly, the newspaper reported, citing several people that it didn’t identify.

The brokerage unit of Sumitomo Mitsui Financial Group Inc., the country’s No. 2 lender, is under investigation for alleged market manipulation.