You'd have to a) convince a majority of your coworkers, and b) have some associated, relevant labor demand. A strike isn't just "I don't want to do this."

I probably shouldn't have complicated things by mentioning an individual, I really don't know if that could even be possible. Imagine I said Republican Party.

The key thing is that for a strike to be declared it has to be called for by the union, it would be unprecedented to call a strike for political action against a party.

It is not a question of what is allowed. The company delivering parcels must fulfill their contracts, but the contracts clearly have stipulations for force majeure. Which a strike is, by the very definition.

What is not clear here? Sweden has very few strikes, but this is a textbook example of one. The postal worker's union have called for their members to refuse to carry out a specific work. This is well within their rights to do. The union calls for this as part of a collective action for their fellow workers.

The company delivering the parcels could call for their employer's union to lock out the workers on strike. But why would they want to escalate the conflict? They too prefer their collective bargaining agreements respected. And they are clearly not in violation of any of their contracts as this is a legal strike.

There are plenty of gray areas within worker's rights, but this is as simple as it could be.