DETROIT (AP) -- General Motors Corp. says about 3,600 workers will be laid off indefinitely beginning early next year as the automaker slows down production at 10 of its assembly plants.

GM spokesman Anthony Sapienza said Friday the production line "re-rates," as they are called, help reduce inventory and adjust to shrinking market demand.

Four line re-rates will take effect Jan. 12 at Michigan plants in Hamtramck and Lansing; Wentzville, Mo.; and Oshawa, Ontario.

More slowdowns will begin Jan. 20 at factories in Bowling Green, Ky.; Lordstown, Ohio; and Spring Hill, Tenn.

Re-rates also will start Feb. 2 in Oakland County's Orion Township in Michigan and Kansas City, Kan., and Feb. 9 at a second Lansing plant.

(Copyright ©2008 by The Associated Press. All Rights Reserved.)