"The companies, the members and the public know what we've been fighting for, and we've been clear: midnight, on the evening of September 14, is the deadline," Fain said in a Facebook* Live address.
"UAW family, this deadline is nearly here. Tonight, for the first time in our history, we will strike all three at the 'big three' at once. We are using a new strategy - a stand-up strike."
Fain also called on select facilities "to stand up and go out on strike at midnight."
Fain identified plants for strikes - a GM facility in Wentzville, Missouri; a Stellantis facility in Toledo; and a Ford plant in Wayne, Michigan.
"For the past 24 hours, we've been actively bargaining with Ford, General Motors and Stellantis. For the first time in our union's history, we had all three companies bargaining right here at the 'Solidarity House,' leading into the final hours of our strike deadline. We've been working hard trying to reach a deal for economic and social justice for our members," Fain said at the time.
US media reports earlier indicated that both sides remained "far apart" on discussions.
The White House previously issued a statement noting that US President Joe Biden spoke with the major US auto companies as well as with Fain to discuss the status of ongoing negotiations concerning wages.
*a social network owned by Meta, banned in Russia as an extremist organization