Italy, Europe's third-largest economy, and Spain, its fourth-largest, could be sliding toward default.
The Dow Jones industrial average lost 151 points, or 1.2 percent, to close at 12,506 Monday. The Standard & Poor's 500 index fell 24, or 1.8 percent, to 1,319. The Nasdaq composite fell 57, or 2 percent, to 2,803.
In the U.S., lawmakers face an Aug. 2 deadline to avoid an unprecedented debt default. The government's surprisingly weak jobs report Friday compounded concerns about the U.S. economy.
Six stocks fell for every one that rose on the New York Stock Exchange. Volume was lighter than usual at 3.5 billion shares.