Stocks closed with their biggest losses of the year as investors worry about fallout from Greece's worsening debt crisis.
Greece is moving closer to defaulting on its debt and could be forced to abandon the euro currency.
The Dow Jones industrial average dropped 350 points, or 2 percent, to 17,596 Monday.
The Standard & Poor's 500 index sank 43 points, or 2.1 percent, to 2,057.
The Nasdaq composite tumbled 122 points, or 2.4 percent, to 4,958.
European markets fell even more. Stocks fell 3.6 percent in Germany and 3.7 percent in France.