Stocks were struggling Thursday, after data pointed to an economy that may have stalled while investors grapple with the euro zone's debt crisis.
A report by private payrolls processor ADP showed private employers created 133,000 jobs in May, fewer than the expected 148,000 while new claims for unemployment benefits rose by 10,000 for the fourth straight weekly increase. The data comes ahead of Friday's key payrolls report.
Commerce Department data showed economic growth in the United States was slightly slower than initially thought as gross domestic product was revised down to a 1.9 percent annual rate from last month's 2.2 percent estimate.
"The markets have become less optimistic and much more accustomed to seeing numbers that are just not impressive," said Peter Kenny, managing director at Knight Capital in Jersey City, New Jersey.
"It is clear the markets are pricing in a substantial slowdown moving forward in terms of GDP growth, employment gains, productivity gains - it's not encouraging for bulls."
The European Central Bank increased pressure for a joint fund to guarantee bank deposits in the euro zone, saying the region needed new tools to fight bank runs as the bloc's debt crisis drives investors to flee risk.
The benchmark S&P index is on pace for its worst monthly decline since September on increasing concern over the euro zone's debt crisis and a spate of tepid domestic economic data.
Reuters contributed to this report.