The number of U.S. temporary workers plunged 19.5% in the fourth quarter of 2008 from the year-ago period, according to the American Staffing Association's quarterly staffing employment survey. The decline exceeded the 18.4% year-over-year decrease measured in the third quarter of 2001.

Staffing firms employed an average of almost 2.5 million temporary or contract workers per day from October through December 2008, the association said. They employed an average of almost 3.1 million per day in the fourth quarter of 2007.

"Daily employment in the staffing industry declined slowly during the first three quarters of the year," said ASA President and CEO Richard Wahlquist. "But then the bottom fell out of the economy, and demand for temporary and contract employees shrank at an unprecedented rate."