The US auto industry reopened many plants last week after a two-month shutdown due to the global pandemic. To ensure safety during the outbreak, companies imposed new safety measures, including screening employees, use of face masks and social distancing.

Ford paused production at its Claycomo, Mo., plant for an hour on Tuesday after a worker tested positive. Work resumed at the plant, which builds the F-150 pickup truck and Transit van, without workers being sent home following a deep cleaning, Ford spokeswoman Kelli Felker said Wednesday.

General Motors and Fiat Chrysler said Wednesday they have had workers test positive since the restart, but have not been forced to idle plants. They did not disclose the number of workers affected.

On Wednesday, a union leader at Ford’s Kentucky Truck Plant said on Twitter a worker there tested positive, but had not worked since May 21. Felker said the plant never closed.

Last week, Ford closed two assembly plants, due to a positive test at its Dearborn, Mich., factory and a parts shortage due to a positive test at a supplier that closed the Chicago plant. It had marked the second consecutive day for closures in Chicago following two positive tests.

United Auto Workers Local 600, which represents hourly workers in Dearborn, last week demanded testing for every worker there and that Ford shut down the plant for 24 hours after a positive test. Ford said the safety of its workers is a top priority and cited the safety measures it has developed in conjunction with the UAW.

In Mexico, Ford told workers it was targeting a May 28 restart at its Hermosillo plant. GM and FCA have restarted operations in Mexico.