New York Attorney General Eric Schneiderman has requested information from Goldman Sachs, Barclays, Credit Suisse and other financial institutions about their use of dark pools, Dow Jones reported Friday.
Dark pools are trading systems set up by banks outside regulated exchanges. Supporters of the pools have argued that they provide liquidity for bigger trades that are harder to execute on stock exchanges.
Earlier this week, the Commodity Futures Trading Commission said it was preparing a proposed rule for automated trading.
The CFTC, which regulates futures and swaps markets, in September put out a study - known as a concept release - into computerized trading that was seen as a possible first step toward drawing up formal rules, according to a Reuters report Tuesday.