Sweden has largely left it to employers and unions to regulate the job market with little interference from politics. For example, there is no minimum wage in Sweden, things like that are collectively bargained by the employers associations and the unions.

A company that comes here and wants nothing to do with unions can't fit into this system, because everything is built on the collective bargaining. Yes, the unions have an important position, you can call it a monopoly, what you miss here is that employers are also organized and have just as much leverage. The central bargaining means that there is literally no risk that a company gets singled out, the local union isn't going to demand a huge pay rise just for Tesla workers.

So there's little risk in signing an agreement with the union, nearly all the other sizable companies in Sweden have done so. On the other hand, no one is going to lift a finger to help Tesla if they continue to be stupid.