There is a concept called Solidarity, which Swedes take very seriously. If one employer chooses to not play fair by the rules of the labor market (which include negotiating with unions in Sweden) then other unions will show Solidarity with the one striking. The unions act with the mandate from the workers. They are not dictatorships.

Historically solidarity between workers is the reason why you only work 8 (instead of 16) hour days. Why workers have vacation days, sick pay, pensions and maternity leave etc.

https://en.wikipedia.org/wiki/Solidarity

I upvoted you because you’re technically right. It’s permitted because it generally leads to good social outcomes at the expense of business profit. This isn’t cost-free, of course. Nothing is. It’s just that Sweden believes the costs are worth it. By the numbers, outcomes for citizens are very good, so I think they’re correct.

By your..."reasoning" voting with your wallet is extortion

"Other people are using their own free will and self determination to undermine a CORPORATION!"

If there's one cartel that should get a pass surely it should be a country-wide labor cartel, right?

Its a free market for labor.

If they aren't operating in explicit coordination, no.

Cartel behavior requires coordination and collusion. If they are just following general social/business practices without having meetings about who to blacklist, then it doesn't meet most definitions.