Unions effectively lost all legal status and recognition in 1991 with the employment contracts act and they have never fully recovered.

Since then it's come back a little with the Employment Relations Act 2000, which is in place today, but there is no sector level bargaining (the new govt immediately repealed the fair pay agreement legislation the last govt passed), it's incredibly easy for employers to pass on collective agreement conditions and sympathy strikes are unlawful (I think this might be the case now in Aus too?). In fact all strikes are unlawful except in bargaining for a collective and for health and safety.

Unions are mostly confined to public sector roles these days, although there are a few in other sectors.