They're not public workers anymore after the liberalisation in the early 2000s. They didn't have the right to strike before that. Because it's a private company, they can strike. Who owns the shares is irrelevant in that context.

From your previous comment, you’re stating you are okay if the union declined to deliver everyone’s mail, which sounds like you’re fine with unchecked power that expresses itself without discrimination.

Correct. I’m not contesting the power to strike, I’m contesting the power to selectively target entities in such strikes.

I don’t know if you thought there was a contradiction there, but I don’t see it.

It doesn’t make sense to consider indiscriminate withholding of services through a strike not “unchecked power,” while selecting specific targets (which is far less disruptive to the market as a whole) as such.

It’s also not an arbitrary choice. It’s a business that’s clearly in dispute with another union, that this union has decided to intervene on behalf of. It’s not like they’re striking against a company that was just minding its own business.

Perhaps there can be labor relations boards and anti-discrimination regulation and such to prevent abuse of selective striking, but this is obviously a situation where everyone is a player and knows what game they’re playing.

There’s nothing arbitrary about it. A worker can’t just declare a strike, that’s illegal. The company the postal company works for, also agreed to these terms.