S&P 500 futures are down 0.4%. Dow Jones Industrial Average futures are falling 0.4%. Nasdaq 100 futures are slipping 0.6%.

Traders are looking ahead to the Friday jobs report, which should give more insight into the strength of the economy and the Fed's next rate move.

One day after hitting an all-time high, US stocks are in retreat Tuesday and volatility is rising on reports that Iran is preparing to launch a ballistic missile attack against Israel within the next 12 hours.