The United Auto Workers (UAW) union is threatening to 'amp' up its strike at the three biggest US automakers
Striking workers re expected to return to work at the three big U.S. automakers. AFP

General Motors was the last of the three big automakers to reach a tentative agreement with the United Auto Workers to end a strike that lasted more than six weeks, according to reports by several news organizations, including Reuters and The New York times.

The United Auto Workers and General Motors haven't officially announced the agreement. Ford reached an agreement on Wednesday and Stellantis on Saturday.

The terms of the new contracts are similar for all three automakers: about 25% salary increases in four and half years and cost of living adjustments, the reports said, citing unidentified people familiar with the discussions.

The preliminary agreements will have to be ratified in a vote by UAW workers, but it allows them to return to work.

The UAW strike started on Sept. 15 and for the first time, it stopped production at plants and distribution centers of the three big automakers simultaneously.

Instead of an all-out work stoppage, the union's strategy this time was to use targeted and escalating walkouts. It started with 13,000 workers on strike and, at its peak, it involved more than 45,000, according to the UAW.

GM said last week that the strike was costing the company about $200 million a week.

On Sept. 26, Joe Biden traveled to Michigan to show support to autoworkers, becoming the first sitting U.S. president to join a picket line.