The United Automobile Workers union said yesterday that it planned to expand its strike against the big three Michigan automakers on Friday if negotiators failed to make substantial progress on new contracts, the New York Times reported. The union ordered workers to walk off the job nearly two weeks ago at three vehicle assembly plants — each owned by one of the companies, General Motors, Ford Motor and Stellantis, the parent of Chrysler and Jeep. Last Friday the union broadened the strike to include spare parts distribution centers owned by G.M. and Stellantis, saying it had made progress in its talks with Ford. U.A.W. President Shawn Fain is scheduled to update members in a video streamed live on Facebook on Friday morning. The union is seeking a substantial wage increase to make up for much smaller raises over the last decade. Each of the companies has offered to lift wages by roughly 20 percent over four years, about half of what the U.A.W. is seeking. The union has demanded other measures, including cost-of-living adjustments, the right to strike to protest plant closures, pensions for more workers and company-paid health care for retirees. The three plants that have been shut down by the strike include a G.M. factory in Wentzville, Mo., a Ford plant in Wayne, Mich., and a Stellantis complex in Toledo, Ohio. They make some of the manufacturers’ most profitable models, including the GMC Canyon pickup truck, the Ford Bronco sport-utility vehicle, and the Jeep Wrangler.