Regulators have delayed action on a proposal to require trading firms to put in place new testing and maintenance checks aimed at preventing market mishaps such as Nasdaq Stock Market’s fumbling of the Facebook public offering.

The holdup comes amid internal conflicts over the scope of the rule within the Securities and Exchange Commission, with Democratic commissioners Kara Stein and Luis Aguilar pushing to extend the rule to more trading activity, among other changes, according to people familiar with the decision. Expanding the rule would provide further protections for investors against technology breakdowns, they argue, but some on Wall Street worry it will impose added costs on trading firms and investors.