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.
On the labour market they are allowed. Unions typically negotiate with employer’s organizations with most businesses as members. Also, labour conflicts are adjudicated in a special court made up by representatives from unions and employer organisations. Kind of like arbitration, but it’s sanctioned by law.
Why? We don’t trust the state to do it better. Neither employees nor employers do.
Short answer is that all parties involved (the State, the Employers and the Employees) want this particular type of cartel to be treated differently from other cartels. The government could change that at any time by passing a law, but they don't because it would be wildly unpopular with everybody.
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.
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.
