U.S. regulators should put on hold CME Group Inc.'s plan to block traders from engaging in transactions with themselves to ensure it sufficiently restricts the illegal trades, said Bart Chilton, a member of the Commodity Futures Trading Commission (CFTC).

CME's plan to prevent wash trades, in which a party buys a contract from itself, should be put under review for additional time and not automatically take effect July 1, Chilton said in remarks prepared for a speech today at the Trading Show Chicago 2013 conference. Chilton, one of three Democrats on the commission, said the agency should take additional steps to vet the CME guidance and determine if other exchanges will have similar or better policies.

“Right now there are simply too many unanswered questions that need to be addressed from an oversight and surveillance perspective, and potentially from an enforcement perspective,” Chilton said. “We need to take a deep breath and ensure that we know, to the best of our ability, what might occur.”