Tesla is suing the Swedish transport agency, accusing it of a “discriminatory attack” on the US electric carmaker, after strike action prevented its new vehicles from getting licence plates in Sweden.

The lawsuit is an escalation in a row that started between the car company and the union representing Swedish Telsa workers, who are calling for collective bargaining rights and have been on strike for five weeks.

The strike called by IF Metall, which has more than 300,000 members in Swedish industry, has attracted multiple secondary, or sympathy, industrial action by unions representing among others postal workers, dock-workers, electricians and painters.

On Thursday Elon Musk, the chief executive of Tesla, decried the secondary action at the postal service PostNord as “insane” after licence plates were prevented from reaching new Tesla cars.

According to the Swedish financial newspaper Dagens Industri, the carmaker said in documents submitted to Norrköping district court on Monday: “This confiscation of license plates constitutes a discriminatory attack without any support in law directed against Tesla.”

Anna Berggrund, director of the Swedish transport agency’s vehicle information department, confirmed that it had received an interim decision from the district court to consent within seven days to Tesla collecting licence plates directly from their sign manufacturer, but that they have not yet decided how to react.

She said: “It appears from the decision that our sign manufacturer has announced that it is prepared to provide the signs directly to Tesla, provided that the Swedish transport agency agrees to this. We at the Swedish transport agency now need to analyse the announcement and assess what consequences this has for us and what measures might need to be taken to implement the decision. It is currently too early to say exactly what that would mean.”

Tesla has reportedly demanded that the district court allow it to collect the number plates from the manufacturer while legal procedures are carried out. This request was granted on Monday, according to Swedish newspaper Aftonbladet, meaning that Tesla can collect its licence plates from the manufacturer. If the Swedish transport agency does not agree to the request within seven days, they will be fined one million kroner (£76,000).

A senior IF Metall official, Veli-Pekka Säikkälä, said: “We note that Tesla has chosen to take the long route, starting legal proceedings. There is a simple and quick way to solve this situation, and that is to sign a collective agreement. As soon as Tesla does that, the conflict ends.

“Swedish law state that authorities should not choose sides in labour market conflicts. We assume that the Swedish Transport Agency will remain neutral in the ongoing conflict, as they should.”

TM Sweden, Tesla’s Swedish subsidiary, is also understood to be pursuing legal action against PostNord for failure to deliver post.

The postal company said the union ST had blockaded mail deliveries from PostNord to TM Sweden as a “sympathy measure for IF Metall”. The right to strike is “constitutionally protected and so strong that it can be considered force majeure”, PostNord added.

A spokesperson said: “We now need to read the lawsuit and form an idea about the content and what it means. First and foremost PostNord is neutral in the conflict.”

The fight for collective agreements – which cover conditions including salary, pension, working hours and holidays – is being portrayed as the largest attempt to save Sweden’s union model from global labour practices in decades. It has been likened to the 1995 strikes at Toys R Us, which Swedish unions won.

Since the start of the Tesla strike, the Swedish global payment firm Klarna has signed a collective agreement with workers to prevent planned action at its Stockholm headquarters. Some commentators have suggested that the strikes affecting the carmaker could restart conversations on the issue at the Swedish division of the streaming firm Spotify.

In Norway, Fellesforbundet, the largest union in the Norwegian private sector, has said it would block Swedish Teslas from coming to the country.

Tesla did not immediately respond to requests for comment.