At least three major companies announced large layoff plans on Thursday.

Sun Microsystems, which has been struggling since the tech-Internet bubble burst in 2000, announced that it plans to cut 4,000 to 5,000 jobs, or roughly 11 percent to 13 percent of its 37,500 employees worldwide.

Heinz, under attack by investor Nelson Peltz, announced plans to cut 2,700 jobs, or 8 percent of its workforce, and close 15 plants this year. The company expects that its cost-cutting efforts will generate $60 million in SG&A savings in fiscal 2007 and another $30 million in 2008.

Schering-Plough announced that it will eliminate 1,100 positions, primarily in 2006. Approximately 600 positions will be cut in Puerto Rico , where the company will phase out some manufacturing operations; another will be eliminated in New Jersey.

Also on Thursday, the Department of Labor reported that the number of workers filing first-time claims for unemployment benefits rose last week to 336,000, an increase of 7,000 from a week earlier. Analysts had anticipated a decline, according to the Associated Press.

The wire service also reported that the four-week moving average for first-time claims now stands at 333,500, the highest level since October.