U.S. electric vehicle manufacturer Tesla has been reported to police in Sweden accused of performing electrical installation work without the necessary registration, the Swedish Electricians' Union said on Wednesday.

There are already tense relations between Tesla and unions in Sweden, where the company has faced prolonged industrial action and its mechanics have been on strike since Oct. 27.

Tesla was not immediately available for comment when contacted by Reuters.

"There is evidence indicating that Tesla is performing electrical installation work at one of its charging stations. This is despite the fact that Tesla is not registered with the National Electrical Safety Board ," the union said in a press release.

The union said that meant Tesla was not legally permitted to carry out electrical installations under Swedish law.

"Since Tesla violates Swedish legislation, we have to react. We can never accept illegal electrical installations," the union's head of negotiations, Mikael Pettersson, said in a statement.

(Reporting by Stine Jacobsen; editing by Jason Neely)