The SEC is moving forward with a new trading rule under a pilot program that will begin in mid-June and until December 10th of this year. Under the program, which all exchanges have agreed to, any S&P stock that changes in price by more than 10% during a 5 minute period would be halted for 5 minutes. These rules would apply between the hours of 9:45 AM and 3:35 PM.
The SEC anticipates voting on the new proposal after a 10-day comment period. If approved, the proposed rule would become permanent. Adjustments to the rule can be made during the pilot program. Those adjustments could include expanding the rule to equities outside of the S&P 500.