WASHINGTON, United States -- The United Auto Workers chief warned Sunday that a historic strike at the top three car manufacturers will expand if the companies do not raise their wage offers in ongoing negotiations.

Stellantis, one of the three, had offered its workers what it called a "highly competitive" wage increase of 21 percent over four years, but UAW President Shawn Fain called that "definitely a no-go."

"If we don't get better offers and... take care of the members' needs, we're going to amp this up even more," Fain told CBS News talk show "Face the Nation," saying General Motors, Ford and Stellantis have "no excuse" for not resolving salary disputes given their massive profits of recent years.

"We're prepared to do whatever we have to do. The membership is ready, the membership is fed up."

The UAW is demanding improved conditions across the board for its workers, including a 40 percent pay raise over the next four-year contract. All three companies have been offering raises of around 20 percent.

A UAW source confirmed that the union held talks with General Motors on Sunday, the third day of the strike, but offered no further details.

The standoff has fed already acrimonious debate in Washington over President Joe Biden’s economic policies ahead of the 2024 election -- and whether he has done enough to avert or resolve the auto dispute.

Only 12,700 of the union's 150,000 workers are currently on strike, but Fain's comments pointed to the possibility of a much broader action, with echoes throughout the economy.

- 2024 presidential race -

Republicans on Sunday tried to tie the strike to voters' concerns on inflation and the Biden administration's overall economic leadership.

"I have no doubt in my mind that all those hard-working autoworkers are living in the same reality as other Americans, and that is that wages are not keeping up with inflation," former vice president Mike Pence said on CNN.

Pence, who is seeking the Republican presidential nomination in the 2024 election, blamed Biden's stewardship for "the worst inflation in 40 years" and added that the administration's electric vehicles push would mainly benefit battery-makers in China.

Pence's former boss Donald Trump, who holds a resounding lead in polls over other Republican presidential aspirants, has been critical of the union's leadership and of Biden's focus on promoting EV manufacturing.

"The auto workers will not have any jobs... because all of these cars are going to be made in China -- the electric cars, automatically, are going to be made in China," Trump said in an interview aired Sunday on NBC's "Meet the Press."

Democrats have lined up solidly behind the autoworkers -- and Biden.

"The president has made it clear which side he is on in this struggle," liberal senator Bernie Sanders said on CNN, adding that Biden had repeatedly said "that a strong labor movement benefits all of us."

On social media, Vice President Kamala Harris said she agreed that "a new contract should promote good middle-class jobs -- and ensure the UAW remains at the heart of our auto economy."

Hakeem Jeffries, the Democratic leader of the House of Representatives, echoed that theme.

"Incredible economic prosperity has been generated for the corporations," he told ABC's "This Week," shortly before heading to Detroit to stand with the workers. "It’s only fair that everyone share in those record profits."