New York Attorney General Eric Schneiderman sued British banking giant Barclays for allegedly lying about how it favors high-frequency players in the firm's stock-trading business.

In one of the highest-profile actions in recent years against a bank for its practices trading stocks, the civil suit filed Wednesday alleged that Barclays engaged in fraudulent activity related to a trading venue known as a dark pool, in which orders are matched anonymously to protect large and sometimes fast-trading investors.