THE United Auto Workers (UAW) union and Detroit’s Big Three car makers resumed talks aimed at ending a strike now in its fourth day.

For the first time in its history, the UAW took on Ford, General Motors and Stellantis at the same time as asking 13,000 of its members to take “stand up” strike action at a factory for each employer on a rolling basis.

The new tactic by the UAW targets specific sites rather than deploying their entire 145,000 Big Three membership.

Stellantis said that it had resumed negotiations with the union on Monday and described the talks as “constructive.”

A spokesman for General Motors said that representatives of the company and the UAW were also continuing to negotiate.

But UAW president Shawn Fain said: “We have a long way to go” and if the companies don’t respond to the union’s demands, “then we will escalate action.”

In a statement, Mr Fain said that more factories could be targeted if “serious progress” towards an agreement isn’t reached by Friday at noon.

He insisted: “We’re not messing around.”

GM said on Monday that 2,000 workers at an assembly plant in Kansas City are “expected to be idled as soon as early this week” because of a shortage of supplies from a plant near St Louis where workers walked off the job on Friday.

Workers at the Kansas City plant build the Chevrolet Malibu and Cadillac XT4.

The strike could begin to affect suppliers and their employees too. CIE Newcor told Michigan officials that it expects a one-month closure of four plants in the state to start on October 2 and idle nearly 300 workers.

In a sign of concern over the strike’s potential economic and political fallout, the Biden administration stepped up its response.

United States Treasury Secretary Janet Yellen said that she is hoping for a quick resolution.

But, she told CNBC: “It’s premature to be making forecasts about what it means for the economy. It would depend on how long the strike lasts and who would be affected by it.”

Meanwhile, Ford’s contract with Canadian union Unifor, which represents about 5,600 workers at three plants in Canada, expired at the stroke of midnight on Monday.

But the union said today that negotiations had been extended for 24 hours after it received a “substantive offer” from Ford.

The union said: “Unifor members should continue to maintain strike readiness.”

Ford said in a statement that it had agreed to continue negotiations beyond the contract deadline.