The Financial Industry Regulatory Authority said today it fined Citigroup Global Markets $300,000 for not properly supervising the commissions it charged on stock and option trades during the period between 2002 and 2007.

According to a FINRA statement, Citigroup didn't make clear that it "generally did not permit brokers to charge commissions that exceeded the rates the firm determined to be reasonable." FINRA also said there wasn't an imposed limitation on the commissions charged on options trades. In short, FINRA said, Citigroup didn't have enough supervisory controls in place at the three branch offices it investigated.

One broker overcharged commission on 27 customers, including one for about $1.2 million. That broker was later barred by FINRA. In settling the case, Citigroup neither admitted nor denied the charges, but consented to the entry of FINRA's findings.