Banks and brokerages are starting to win more battles with big stock-market operators over the cost of data, threatening a lucrative revenue stream for the New York Stock Exchange and Nasdaq.

The Securities and Exchange Commission has recently ratcheted up scrutiny of the stock-price feeds sold by exchanges that are used by retail investors, Wall Street banks and high-speed trading firms alike. Several recent SEC decisions represented wins for brokers and traders which have criticised rising data costs.