The union has used an innovative approach to step up pressure on large companies and win substantial wage gains.

The deal, reported on Monday but not yet confirmed by UAW or GM, comes shortly after the union reached tentative agreements with auto giants Stellantis and Ford.

The agreements are the result of a six-week strike that targeted the “Big Three” automakers and won record wage gains and improved benefits, one of the most substantial victories for striking workers in years as organised labour gains traction in the United States after decades of decline.

The Associated Press news agency reported that the deal with GM will include a 25 percent pay increase, with cost-of-living adjustments that will bring the wage bump to 30 percent over the lifetime of the contract, citing two sources briefed on the deal.

The union had reached tentative agreements with Ford and Stellantis last week, and ratcheted up pressure on GM by expanding the strike to a lucrative Tennessee factory over the weekend, with nearly 4,000 workers walking off the job at GM’s largest North America plant on Saturday.

The UAW used a strategy that included gradually expanding the strike to larger and more profitable facilities, slowly squeezing critical pressure points and allowing workers to push for concessions at the negotiating table.

UAW leader Shawn Fain, who helped orchestrate the strategy, has framed the strike as a fight against widening inequality that has helped spur an uptick in labour organising in a wide variety of sectors, from nurses and Starbucks baristas to graduate students and auto workers.

Fain called the union’s deal with Ford “a turning point in the class war that has been raging in this country for the past 40 years”.

“We were being left behind by an economy that only works for the billionaire class,” he said in a livestream discussing the deal.

The prospective contracts must now be ratified by rank-and-file workers.

Asked about the potential deal on Monday, US President Joe Biden said “I think it’s great.”

Biden has sought to portray himself as the most pro-union president in decades, joining striking autoworkers on a picket line in late September.

“They [the auto companies] are doing incredibly well. And guess what? You should be doing incredibly well,” Biden said in a speech to the workers at the time.

A different union in Canada also reached a tentative deal with Stellantis on Monday following a brief strike, winning an hourly wage increase of about 20 percent.

The US news outlet Reuters reported that striking GM workers would return to work following an official announcement of the agreement, citing two anonymous sources.