Stocks are tumbling as investors worry that Greece won't qualify for a new installment of emergency funds in time to avoid defaulting on its debt.
Investors also appear pessimistic about a Federal Reserve policy decision expected Wednesday. The Fed has hinted it might take new economic stimulus measures. But many analysts think they won't be announced this week.
President Barack Obama on Monday called for $1.5 trillion in new taxes to help reduce the U.S. deficit, saying "we can't just cut our way out of this hole."
In midmorning trading, the Dow Jones industrial average is down 185 points, or 1.6 percent, at 11,324. The Standard & Poor's 500 index is down 19, or 1.6 percent, at 1,197. The Nasdaq composite is down 22, or 0.9 percent, at 2,599.