General Motors, Ford Motor Co. and Fiat Chrysler Automobiles are targeting May 18 to resume some production at their U.S. factories after shutting down plants in March due to the coronavirus outbreak, the Wall Street Journal reported.

Executives from the companies in recent days tentatively settled on the timeline following talks with UAW leaders and Michigan Gov. Gretchen Whitmer's office, the Journal said on Monday, citing people familiar with the plans.

A UAW spokesman late Monday said the union had not been notified by the automakers of a production restart date.

The head of the UAW last week warned it was "too risky" to reopen auto plants and Michigan's economy in early May, citing risks to workers.

The companies are working with the union on drawing up safety protocols for reducing exposure risk for workers, but haven't finalized those terms yet, according to the WSJ report.

In a statement late Monday, Ford said it has not yet determined when it will resume North American production.

"We are continuing to assess public health conditions, government guidelines and supplier readiness to determine when the time is right to resume production," Ford's statement said. "Meanwhile, Ford and the UAW continue working closely on initiatives to keep the workforce safe when we do restart our plants."

GM said Monday it still has no firm restart date.

FCA said that it's is re-evaluating its plans to resume its North American operations in light of updated state stay-at-home orders and "will communicate new restart dates in due course." FCA had targeted May 4 to resume some production.

Michael Martinez, Hannah Lutz and Vince Bond Jr. of Automotive News contributed to this report.