This isn't possible for Tesla because PostNord currently has the exclusive right to deliver license plates - they literally can't hire any other courier company to do it.
They could, the next time the contract is up for renegotiation.
It would require however that there are other couriers that fulfill their safety requirements with the logistic infrastructure to deliver to the entire country. That's not likely. But entirely within the realm of possibility that someone with deep pockets could start one.
However it would not make any difference for Tesla, as that courier would also be unionized. Few other companies would do business with them otherwise, as Tesla is about to find out.
They can, they can just face potential legal issues. Which Tesla would claim PostNord is in breach of contract for failing to deliver the license plates. PostNord would claim the right to strike and Tesla should claim it's PostNord's responsibility to find others willing to do the job in the place of striking workers.
It would require however that there are other couriers that fulfill their safety requirements with the logistic infrastructure to deliver to the entire country. That's not likely. But entirely within the realm of possibility that someone with deep pockets could start one.
However it would not make any difference for Tesla, as that courier would also be unionized. Few other companies would do business with them otherwise, as Tesla is about to find out.