Chairman Mary Schapiro said she is asking Securities and Exchange Commission staff to propose a rule that will require exchanges and market centers to ensure the capacity and integrity of the systems they operate.

The rule will call for market operators to have specific programs in place to ensure the capacity and integrity of their trading systems.

She said SEC staff will convene a roundtable "in the coming weeks" to discuss this and other steps that can be taken to head off an incident such as Wednesday's flood of erroneous orders from Knight Capital. She called that event 'unacceptable.'

She said, however, that "reliance on computers is a fact of life" and said, even after a recent string of technical mishaps since the May 6, 2010 Flash Crash, U.S. markets remain "the most resilient, efficient, and robust in the world."

She said circuit breakers that have been put in place in the last two years as well as clear guidelines on what trades can be broken and when have helped.

"In addition, existing rules make it clear that when broker-dealers with access to our markets use computers to trade, trade fast, or trade frequently, they must check those systems to ensure they are operating properly'' she said. "And, naturally, we will consider whether such compliance measures were followed in this case.

TD Ameritrade and Scottrade said they would resume sending orders to Knight.