Man, the US really are a dystopia.

There are actually protections for striking according to the NLRB "depending on the purposes and means of the strike action."

I believe if it's an unsanctioned wildcat strike they can fire without it being retaliation, but if it's a strike backed by the NLRB they have to prove it isn't retaliation and I don't think the days gone by an official strike counts here. I could be wrong but that is what I remember about wildcat strike differences

That's interesting - in Australia we do have 'protected action' that can be taken when bargaining. Basically each workplace in a union has a vote to strike (endorsed by the fair work commission) and if it gets up any action taken is protected from retaliation.

It depends on the kind of strike. Workers that strike over a company's unfair labor practice are protected from permanent replacements. This is not that tho. While they are far apart, I don't think they can accuse the companies of refusing to negotiate.

Of course if the union wins the strike then no replacement.