HOFFMAN ESTATES, Ill. — Sears Holding Corp. plans a "mass layoff" of 250 workers at its headquarters in this Chicago suburb, according to a report filed with the state's Department of Commerce and Economic Opportunity. The state defines a mass layoff as 250 or more full-time employees or at least 25 employees if they make up at least one-third of the employer's work force. According to a 2004 state law, employers with at least 75 full-time workers must give 60 days notice to workers and the state of mass layoffs or a plant closing. Sears Holding, which was created last week through a $12.3 billion acquisition of Sears, Roebuck and Co. by Troy, Mich.-based Kmart Holding Corp., filed the report this week. The notice was posted on the department's Web site Thursday. Sears spokesman Chris Brathwaite declined to comment on the filing and said it has not been determined how many people will lose their jobs. But the commerce department's Web site says 250 workers would be affected at the company's headquarters.