From the bls.gov
In 2008, the total number of mass layoff events, at 21,137, reached its highest annual level since 2001.
The total number of initial claims for unemployment insurance benefits due to mass layoffs, at 2,130,220, reached its highest annual level since 2002.
Manufacturing accounted for 33 percent of all mass layoff events and 41 percent of initial claims filed during 2008. The number of manufacturing claimants was highest in transportation equipment manufacturing, 323,676, followed by food manufacturing, 72,081, and wood product manufacturing, 56,374.
The Midwest reported the highest number of initial claims filed due to mass layoffs during 2008 (676,591). Layoffs in transportation equipment manufacturing accounted for 30 percent of the claims in the Midwest.
These data are from the Mass Layoff Statistics program. See "Mass Layoffs in December 2008 and Annual Totals for 2008," (PDF) (HTML) news release USDL 09-0094, for more information. Each mass layoff event involves at least 50 persons from a single establishment.