The Dow Jones Industrial Average fell 82.88 points (0.68 percent) to 12,148.23 in the first minute of trade.
The Nasdaq Composite tumbled 30.61 points (1.12 percent) to 2,706.54, while the S&P 500 index, a broader measure of the markets, slid 11.20 points (0.87 percent) to 1,273.88.
"US stocks are set to start the week on a sour note, thanks to fading optimism over last week's highly anticipated eurozone debt deal," said Andrea Kramer at Schaeffer's Investment Research.
"Furthermore, it appears Wall Street is taking a cautious approach to a week chock-full of notable items on the agenda, including a summit of Group of 20 leaders, a press conference with Federal Reserve chairman Ben Bernanke, and an onslaught of unemployment data."
The Fed is slated to announce its latest monetary policy decision Wednesday, while on Friday the government reports October job numbers.
Adding to the uncertainty on Wall Street were reports that brokerage firm MF Global is on the brink of filing for bankruptcy protection.
The three stock indexes had closed narrowly mixed Friday but gained more than three percent over the week, buoyed by news Thursday that European Union leaders reached a eurozone debt deal.
Copyright AFP (Agence France-Presse), 2011