Stealing or withholding property is not a legitimate form of striking. If you don't want to deliver something, fine, but you can't stop someone from picking it up themselves
Welcome to Sweden, where unions and corporations determine the rules, and the government tries to stay out of it.
Which is actually a great system in my opinion. However, the government does still have to step in if the parties break law.
They are not stealing or withholding the property - they are refusing to deliver it. They are not stopping someone from picking it up, postnord is. It would be weird for any carrier to allow outsiders to enter their premises.
There are two defendants: postnord and the state agency.
Postnord should not refuse to let Tesla collect the plates that Postnord has. That would be theft