DETROIT — Ford, Fiat Chrysler, Honda and Toyota took steps Thursday to restart North American factories that have been closed to protect workers from the coronavirus.

The plants would reopen in early or mid-April, restoring the largest source of cash for automakers that generally book revenue when they ship vehicles to dealerships.

Auto companies, like other businesses, are trying to manage their way through the coronavirus crisis, which has forced factories to close amid employee concerns that they could catch the virus while working close to others.

Ford said it wants to reopen five North American assembly plants, starting with one in Mexico on April 6 and continuing with four in the U.S. on April 14. The move was immediately met with skepticism by the United Auto Workers union, which represents 56,000 Ford factory workers.

“The UAW continues to review with great caution and concern decisions being made about restarting workplaces, especially at advanced dates,” union President Rory Gamble said.

Honda wants to reopen U.S. and Canadian factories on April 7, a week later than originally planned, while Toyota plans to restart North American plants on April 20. Fiat Chrysler intends to reopen U.S. and Canadian factories April 14 depending on state restrictions and plant readiness. General Motors says it hasn’t decided yet when factories would restart. Most automakers said they would monitor the virus and adjust decisions if needed.

The factory decisions contrast with Italy, which on Thursday expanded a nationwide lockdown to include most heavy industry. Auto plants in Italy, which leads the world in virus deaths, already had been closed voluntarily.

The automakers’ moves in the U.S. come as new auto sales are expected to fall dramatically for the month of March. Edmunds.com expects March sales to fall nearly 36% from a year earlier.