"There's fear entering certain parts of the market, and we're seeing a risk adjustment taking place," said Paul Mendelsohn, chief investment strategist with Windham Financial. "This shift could be foreshadowing something bigger, as everyone could run for the door at the same time. Once markets start picking up momentum, they tend to keep moving because everyone's on the same side." Virtually every sector finished with losses. Among the worst decliners, the Amex Oil Index dropped 3.5%, the Philadelphia Utility Index slumped 3.5%, the Nasdaq Financial Index fell 3%, and the KBW Bank Index lost 3%. Apple ( AAPL), which will post earnings late Wednesday, contributed to the tech sector's slide amid speculation the iPhone maker will miss sales targets for the new gadget. Shares tumbled 6.1% to $134.89. Trading curbs were put into effect on the New York Stock Exchange for the first time since March 13, when subprime fears surrounding New Century ( NEWCQ) and Accredited Home Lenders ( LEND) first became a force and sank the major averages. About 3.91 billion shares changed hands on the NYSE, as decliners toppled advancers by a 9-to-1 margin. Volume on the Nasdaq reached 2.46 billion shares, with losers outpacing advancers 5 to 1. Another setback came from General Motors ( GM), which, according to a report in The Wall Street Journal, is having trouble raising debt for its Allison engine unit. The division is trying to raise funds to complete a leveraged buyout. GM shed 47 cents, or 1.3%, to $34.65.