General Motors and Ford Motor on Monday said they are indefinitely laying off another 500 workers at four Midwestern plants because of the impact on some of the facilities of the United Auto Workers strike in its 18th day.

Ford on Monday said it was furloughing a total of 330 workers at its Chicago Stamping and Lima, Ohio Engine plants, while GM furloughs include 130 at its Parma, Ohio Metal Center and 34 at its Marion, Indiana Metal Center.

The UAW on Friday said it would strike at GM’s Lansing Delta Township assembly plant that makes the Buick Enclave and Chevrolet Traverse SUVs after previously striking at GM’s Missouri assembly plant and 18 parts distribution centers.