AMC threatened the demise of its Kenosha plant.

American Motors Corp. said it would close its only U.S. car assembly plant if the United Auto Workers demand major changes in the pay-back of worker concessions. The statement was made to UAW leaders meeting at a Milwaukee hotel, AMC said. A similar message was delivered by mail over the weekend to workers in nearby Kenosha, Wis., who assemble the Renault Alliance and Encore subcompact cars, and to workers at AMC’s Milwaukee metal stamping plant and Jeep assembly plant in Toledo, Ohio.