Bit of clarification here, anyone working at Tesla in Sweden are free to join the union, Telsa can not stop them nor terminate them for that.

It is up to the individual.

And even on a individual level you can join a strike if the union wants it, and again Tesla can not do anything about it. Strong labour laws in Sweden.

What the union is trying to do here is make Tesla the company to sign a collective labour agreement.

These agreements are voluntary, and you can ask ChatGPT what all benefits/drawbacks are with them. In any case Tesla doesn't want it but let the it be an individual decision.

Well, by law voluntary, but the unions will force it.