The New York Stock Exchange and NYSE Amex Cash Markets invoked a rule to smooth trading at the market open on Tuesday as futures pointed to a sharp drop in the major indexes.

Rule 48 allows the exchange to suspend price indications that help determine the floor price at the open during regular sessions. Bypassing the requirement helps speed the beginning of trading.

Among the triggers for invoking the rule are substantial activity in the futures market before the open, according to the exchange's website.

Stock index futures pointed to a sharply lower open, tracking European equities on renewed fears the euro zone's sovereign debt crisis was worsening.

S&P 500 futures fell 27.1 points and were below fair value, a formula that evaluates pricing by taking into account interest rates, dividends and time to expiration of the contract. Dow Jones industrial average futures lost 226 points and Nasdaq 100 futures dropped 38.25 points.

(Reporting by Rodrigo Campos; editing by Jeffrey Benkoe)