The United Auto Workers (UAW) union declared a strike targeting Ford, General Motors and Stellantis, in a bid to put pressure on the carmakers to grant higher pay and make other improvements in new labour agreements.

It comes at a time of broader labour unrest and casts a cloud of uncertainty over an industry that accounts for 3% of the national economy.

The two sides are negotiating over issues such as pay, days off and cost of living adjustments,as well as systems that pay newer and “temporary” hires less for comparable work.

UAW president Shawn Fain has cast the fight as part of a broader battle over economic justice and the billionaire class.

The UAW opened negotiations seeking a 40% pay rise over the four years of the contract.

The union has rebuffed claims that the figure is outlandish, noting double-digit jumps in the pay packages for company bosses, a surge in profits – and money the companies have spent buying their own shares – as well as decades of declining pay power in the industry, including in recent years, when prices surged.

The chief executives of all three companies had pay packages last year worth more than $20m.

The fight also comes as the industry is investing heavily in electric vehicles. The union is worried about that shift, since producing such cars requires fewer workers and currently involves non-union labour.