UAW President Shawn Fain said the union would not expand its strike against the Big Three automakers on Friday, but that the UAW stood ready to add more workers to the picket lines at any time as its labor action enters a new phase.

"We are prepared at any time to call on more locals to stand up and walk out," Fain said on a livestream update on negotiations.

The announcement marks a tactical shift. Fain said. Previously the UAW had announced strike expansions on Fain's weekly Friday updates. But now, as part of the union's strategy to keep the automakers off balance, Fain said strike expansions could come at any day of the week, at any time.

On Wednesday evening the union added Ford's largest factory, the Kentucky Truck Plant in Louisville, to its list of strike targets, as 8,700 UAW members joined the strike that started on September 15.

It is Ford's largest factory in the world, assembling heavy duty pickup trucks and full-size SUVs, producing $25 billion in annual sales, or about one-sixth of its revenue. It also produced an estimated $150 million in profits a week, according to an estimate from Colin Langan, auto analyst at Wells Fargo.

This is a developing story. It will be updated.