A second General Motors Corp. plant that builds passenger cars will soon be affected by the strike at American Axle & Manufacturing Inc.

GM will idle a third shift starting April 21 at its Oshawa, Ont. car plant, where the automaker builds one of its staple vehicles, the Chevrolet Impala full-size sedan, GM Spokesman Stew Low said. Two Saturday shifts also will be cancelled. The plant also builds the Buick Lacrosse sedan.

Most of the two dozen GM factories affected by a parts shortage created by the strike, now entering its seventh week, produce slow-selling large trucks and SUVs or parts for those vehicles.

The Impala is a key vehicle for GM, which sold nearly 72,000 of the sedans through March of this year. It's GM's best-selling auto behind the Chevrolet Silverado pickup, and was the nation's seventh most-purchased vehicle in March.

Oshawa car is the second sedan plant to be affected by the strike, which began Feb. 26 after 3,650 union members at five plants in Michigan and New York walked off the job after their previous contracts expired. GM's Detroit-Hamtramck plant, which builds the Buick Lucerne and Cadillac DTS sedans, was idled March 31.

Another important car factory, in Lordstown, Ohio, could go down in a matter of days or weeks, according to local UAW officials. That factory builds the Chevrolet Cobalt and Pontiac G5 small cars.