The United Autoworkers Union (UAW) in the US has suffered a defeat in its campaign to expand membership to car factories in the American south.

Mercedes-Benz workers in Alabama voted 2,642-2,045 against joining the union, with 56% of eligible ballots cast opposed, according to the National Labor Relations Committee.

The outcome is a blow to an effort the union started last year, hoping to seize on a wider resurgence in worker activism and build on the momentum it had gained after winning big raises for workers at General Motors, Ford and Stellantis.

The UAW notched its first victory at a Volkswagen factory in Tennessee last month.

But its efforts in Alabama met with stiff resistance, including from state and local politicians such as Governor Kay Ivey, who called the union campaign a “threat from Detroit” that put the state’s car industry at risk.

Regulators are also investigating union complaints that the company broke labour law in its opposition to the effort, including by barring distribution of union materials and punishing staff who discussed or supported the effort.

Mercedes has denied the claims.

It said before the vote that it respected its staff’s right to choose, while believing that “open and direct communication with our Team Members is the best path forward to ensure continued success”.

After the results were announced, the company said its goal had been “to ensure every eligible team member had the opportunity to participate in a fair election”.

“We thank all team members who asked questions, engaged in discussions, and ultimately, made their voices heard on this important issue,” it said in a statement.