OSLO, Dec 6 (Reuters) - Norway's Fellesforbundet, the country's largest private sector labour union, said on Wednesday it could from Dec. 20 start blocking any transport of Tesla cars meant for the Swedish market.

Swedish unions have taken industrial action against Tesla since October in a bid to force the car manufacturer to sign collective bargaining agreements with mechanics.

"We consider blocking transportation of Tesla cars through Norway to Sweden unless Tesla reaches an agreement with Sweden's IF Metall union," a spokesperson for the Norwegian union told Reuters.

On Tuesday, Denmark's 3F labour union also said it would support the Swedish mechanics by refusing to unload or transport cars made by the U.S. auto company for customers in Sweden.

The Norwegian and Danish unions said their actions would only affect cars that are meant for the Swedish market. (Reporting by Nerijus Adomaitis, editing by Terje Solsvik)