Negotiations between the United Auto Workers (UAW) and Big Three U.S. automakers continued Tuesday, as U.S. President Joe Biden visited a picket line outside a General Motors parts distribution center in the U.S. state of Michigan and Republican Donald Trump announced a visit to the state Wednesday to show his support to autoworkers.

Each 2024 presidential candidate, tied in the polls over a year out from the election, is seeking to win over blue-collar voters and their dueling trips have ensured that the strike will now become a political battleground, reports said.

"You made a lot of sacrifice. You gave up a lot when the companies were in trouble. Now, they're doing incredibly well... You should be doing incredibly well, too," Biden said on the 12th day of the union's strike, amid the applause from the striking workers. "You deserve a significant raise you need and other benefits... It's time for them to step up for us."

"Wall Street didn't build the country," Biden said. "The middle class built the country, and unions built the middle class. That's a fact. Let's keep it going."

This is the first time in at least a century for a sitting president to visit a labor union's picket line, at the invitation of UAW President Shawn Fain, the Detroit News quoted the White House as saying on Tuesday.

"The White House has been toeing a careful line during the strike, voicing support for the workers and a pay increase but declining to specifically endorse the union demands," CNN reported on Tuesday.

Fain joined Biden at the picket line, and he thanked Biden for coming, saying the president "will do right by the working class."

Former U.S. President Donald Trump is set to make an address Wednesday at an auto supplier in Macomb County, Michigan, to show his support to the autoworkers.

Trump's support among union members has increased as Biden's has fallen in recent months, according to Michigan polling company EPIC-MRA. Trump led Biden 46 percent to 43 percent among union members in an August survey, after Biden led Trump 51 percent to 42 percent in June, according to Bernie Porn, president of EPIC-MRA.

In response to the UAW strike, Ford in a statement conveyed a commitment to reaching an agreement with the union.

"Ford and the UAW are going to be the ones to solve this by finding creative solutions to tough issues together at the bargaining table," the statement said. "We have a shared interest in the long-term viability of the domestic auto industry, the industrial Midwest and good-paying manufacturing jobs in the U.S. That's what's at stake, so we are going to stay focused on reaching a deal that is fair to our employees and enables us to invest and grow."

GM said in a statement that its "focus is not on politics but continues to be on bargaining in good faith with the UAW leadership to reach an agreement as quickly as possible that rewards our workforce and allows GM to succeed and thrive into the future."

GM has presented five "historic" offers covering wages and job security.

"We value our workforce, and understand the impact a strike has on our employees, communities and the economy – nobody wins," the statement said.

Stellantis in a statement said the company "presented a record offer" with a 21.4-percent compounded wage increase, $1 billion in retirement benefits and inflation protection and job security measures.

"Unlike the non-unionized transplants and EV startups who comprise the majority of the U.S. market, Stellantis relies on the collaboration between management and labor to ensure that our company remains competitive, and therefore sustainable," the statement said. "It requires a balanced agreement that fairly rewards our workforce for their contribution to our success, without significantly disadvantaging Stellantis against our non-union competitors."

"We stand ready to sign a record contract that positions our company to continue providing good jobs here at home and be the winner as the U.S. transitions to an electrified future," the statement said.

The UAW went on strike on September 15 at three select facilities of Ford, GM and Stellantis, and expanded the strike to 38 GM and Stellantis facilities on September 22. Nationwide, 18,300 UAW autoworkers at 41 Ford Motor Co, GM and Stellantis NV facilities in 20 states are on strike, asking for higher wages, pensions for all workers and the elimination of the tiered wage systems.

Michigan consulting firm Anderson Economic Group LLC estimates that in the first week prior to the expansion, the strike caused an economic loss of more than $1.6 billion from lost wages, production and other impacts from the walkouts and layoffs at suppliers and feeder plants.