Workers and management from the iconic "Big Three" auto giants were to face off at the negotiating table Saturday on the second day of a strike threatening to disrupt the economy and rock the 2024 presidential election campaign.

After a failed last-minute push by General Motors, Ford and Stellantis to produce an agreement before the deadline late Thursday, United Automobile Workers members walked out Friday.

They appeared determined to stick with the action, even as Ford quickly announced that ripple effects from the walkouts meant temporary layoffs of 600 jobs.

UAW President Shawn Fain said late Friday that it wasn't true "negotiations have broken down."

However, he added that "our members and allies are standing strong at the picket lines. Anyone who wants to stand with us can grab a sign and hold the line."

"Tomorrow, we expect to be at the bargaining table," he said. "All three companies have received a comprehensive counteroffer from our union, and we await their response."

Only about 12,700 of the 150,000 workers represented by the UAW are on strike. However, the decision by the rival companies' employees to act in unison sent a powerful message in their battle for pay increases of 40 percent.

The upheaval in the crucial sector, involving brands like Jeep, threatens the US economy in a period of strong growth and inflationary pressure.

President Joe Biden, who is seeking reelection next year, gave his backing to the strikers, saying he understood their "frustration."

Speaking on live TV from the White House, Biden said workers had not been able to benefit from enormous corporate profits, which exceeded $20 billion for the three giants in just the first half of 2023.

"The companies have made some significant offers but I believe they should go further to ensure that record corporate profits mean record contracts for the UAW," the Democrat said.

Underlining the unions' political clout, leftist Senator Bernie Sanders and Michigan's Democratic governor, Gretchen Whitmer, addressed a crowd of strikers late Friday.

"This is the richest country in the history of the world and families in this country and families in the auto industry should not have to live under this kind of stress," Sanders said.

- Hourly workers left behind -

Fain said the union would strike at one plant at each company: a GM factory in Wentzville, Missouri; a Stellantis facility in Toledo, Ohio; and a Ford plant in Wayne, Michigan, but only in the final assembly and paint operations.

The threat however was clear that the strike could expand.

Many hourly workers say the auto giants must produce significantly better packages to make up for what they call meager wages and benefit cuts after the 2008 financial crisis, when both GM and Chrysler, now part of Stellantis, underwent bankruptcy reorganizations.

"This company has been making money off of us for years," said Paul Sievert, who has worked at Ford's Wayne plant for 29 years. "I think it's time that we got back."

Sticking points also include raising pay and benefits for junior employees to match the level of more seasoned workers, who currently make a top rate of around $32 an hour.

General Motors upped its offer Thursday, lifting a proposed wage increase to 20 percent. The company had previously proposed an 18 percent rise, according to the UAW.

In a statement Friday, GM said it would "continue to bargain in good faith with the union to reach an agreement as quickly as possible."