Negotiations between the United Auto Workers (UAW) and the Big Three U.S. automakers continued Saturday as the union's strikes entered its 9th day.

On Friday, UAW added 38 General Motors Co. and Stellantis NV parts distribution centers to the strike, involving 5,600 workers.

The union is pushing for significant wage increases, an end to the tiered wage system, and cost-of-living increases, among other demands, the Detroit News reported on Saturday.

Ford Motor Co. is spared from the expansion of the strike as talks have progressed.

UAW President Shawn Fain said they received contract improvements from Ford, including the move to give workers at two targeted Ford plants the same wage scale as assembly plant workers, and the right to strike over plant closures.

Fain also cited improvements to the profit-sharing formula Ford has offered, but failed to mention any movement on wages.

The latest known offer from Ford was a 20-percent wage increase over the length of the contract, in line with what GM and Stellantis have offered. The union's last proposal was a 36-percent wage hike.

Stage for political fight

U.S. President Joe Biden plans to visit Michigan on Tuesday to show support for UAW workers on strike, a visit coming on the eve of a similar trip by his right-wing 2024 election challenger Donald Trump.

"It's time for a win-win agreement that keeps American auto manufacturing thriving with well-paid UAW jobs," local media quoted Biden as saying in a statement posted on X, formerly known as Twitter.

Biden's announcement guaranteed that a strike already promising to be a potentially major disruption to the U.S. economy will now be the stage for a fierce political fight. 

The UAW earlier Friday had invited Biden to come – an invitation that would have been politically difficult to turn down.

The day after Biden's stopover, his Republican rival Donald Trump, who is likely to face him for a rematch next year, will also visit the strikers.

Support for trade unions has been a hallmark of Biden's presidency. However, the Democrat is also the driving force behind government-funded efforts to spark a historic shift in the automobile industry to more environmentally friendly electric vehicles.

Biden must now walk a thin line between maintaining his pro-union stance and hoping for a quick resolution to the strike before it can weaken the overall strong U.S. economy.

Trump, meanwhile, is keen to eat into Biden's union base. Reacting to Biden's announcement, Trump spokesman Jason Miller said on X that the president was making "nothing more than a cheap photo op."

"The only reason Biden is going to Michigan on Tuesday is because President Trump announced he is going on Wednesday," Miller added.

(With input from agencies)