"The market-order collar is an additional protection that complements those already in place and addresses a specific issue highlighted by the flash crash -- market orders that were executed at anomalous prices in electronic markets. The new collar is designed to help limit potential harm from extreme market volatility by preventing trades from occurring a specified percentage away from the last trade price," said Joseph Mecane, Executive Vice President and Co-Head of U.S. Listings and Cash Execution. "We will continue working closely with the SEC, other markets and market participants toward the goals of further strengthening the markets' safety net and rebuilding investor confidence in our national market system."

The new collar will prevent market orders to buy stock from executing or routing to another trading venue at a price above the collar. Conversely, market orders to sell will not execute or route at a price below the trading collar. The collar for issues priced $25 or less will be 10 percent above or below the last trade price; for issues priced above $25 up to and including $50, the collar will be 5 percent; and for issues above $50, the collar will be 3 percent. These limits also will help prevent erroneous trades from inadvertently triggering the individual-stock circuit breakers introduced last month, and are consistent with those in the newly implemented rules concerning the cancellation of erroneous trades.