Stock exchanges in the U.S. have joined forces to seek a postponement of rules intended to address the 2010 "flash crash," sources said. SIFMA has also sent a letter to the Securities and Exchange Commission, raising concerns that market participants might not have enough time to adapt their technology to the changes. "In today's markets, with everything so automatic, every change requires some type of systems and coding changes," said T.R. Lazo, managing director and associate general counsel at SIFMA. "We want to make sure we do everything we can to get it right." Take advantage of early-bird rates for SIFMA Tech 2013 -- June 18 to 19 -- New York City.