Companies like miners, banks and chemical makers, whose fortunes are most closely tied to the prospects for growth, fell the most. That's a sign investors are becoming less confident in the U.S. economy.

The troubling data released Wednesday included weak hiring at private companies, orders to U.S. factories that were weaker than expected and sluggish job growth in the service sector.

Investors have become increasingly sensitive to economic reports in the last two weeks. They are trying to anticipate when the Federal Reserve will pull back on its $85 billion of bond purchases a month. That program has supported markets this year, and on some days stocks have even rallied on speculation that an ailing economy would ensure the stimulus will remain in place.