In what has been portrayed as the largest fight in decades to save Sweden’s union model from global labour practices, the powerful trade union IF Metall has been leading a strike across eight Tesla workplaces in Sweden for five weeks.

It is the first time workers for the US carmaker have gone on strike and on Thursday, Musk, the tech billionaire and chief executive of Tesla, made his feelings clear, writing on X, formerly Twitter: “This is insane.”

He was responding to a social media post about secondary, or sympathy, strikes by Swedish postal services that are preventing licence plates reaching new Tesla cars.

The Tesla strike has attracted secondary action from eight other unions and is threatening to spread to neighbouring Norway, where Fellesförbundet (the United Federation of Trade Unions), the country’s largest private sector union, said it was prepared to take sympathy action.

The strike has gained support from transport and harbour workers, who have refused to load or unload Tesla cars in all Swedish ports; electricians who have refused to carry out service or repair at Tesla’s workshops; and charging stations and painters, who will not work on Tesla cars. Other sympathy strikes include those by service and communication workers, who have stopped distributing post and shipments to Tesla.