(Bloomberg News) The four largest U.S. stock market operators asked the Securities and Exchange Commission to delay implementation of rules governing how brokers send orders to venues, including a ban on unsupervised market access given to some high-frequency traders.

NYSE Euronext, Nasdaq OMX Group Inc., Bats Global Markets and Direct Edge Holdings Inc. asked the regulatory to extend to Nov. 30 the date by which broker-dealers routing orders for other securities firms must comply with the rules. The current deadline is July 14.

The SEC in November proposed banning unfiltered or "naked" access to markets, in which brokers allow clients to make unsupervised trades on stock exchanges, a practice that Boston-based research firm Aite Group LLC said accounted for two of every five shares changing hands in the U.S. in 2009. The rule applies to all forms of securities trading, including the routing of orders to markets.

Richard Adamonis, a spokesman for NYSE Euronext, declined to confirm or comment on the letter. Stacie Fleming of Lenexa, Kansas-based Bats, declined to comment. Robert Madden of Nasdaq OMX in New York couldn't immediately be reached for comment. Michael Boccio of Sloane & Co., which represents Direct Edge, said the market operator co-signed the letter from the exchanges. Direct Edge is based in Jersey City, New Jersey.

John Nester, an SEC spokesman, declined to comment on whether implementation would be delayed.