New York's top law enforcer has opened a broad investigation into whether U.S. stock exchanges and alternative venues provide high-frequency traders with improper advantages, a person with direct knowledge of the matter said.

Attorney General Eric Schneiderman is examining the sale of products and services that offer faster access to data and richer information on trades than what's typically available to the public, according to the person. Wall Street banks and rapid-fire trading firms pay thousands of dollars a month for these services from firms including Nasdaq OMX Group Inc. and IntercontinentalExchange Group Inc.'s New York Stock Exchange.

The attorney general's staff has discussed his concerns with executives of Nasdaq and NYSE and requested more information, said the person, who asked not to be named because the inquiry hasn't been announced. Schneiderman's office is also looking into private trading venues, known as dark pools, and the strategies deployed by the high-speed traders themselves.