Jetstar NZ pilots, I believe, work for a NZ registered company. They pay income tax to the NZ IRD. They work under a contract that complies (I presume) with NZ labour laws. Australian unions get very little say in what goes on in other countries.
Why do you think they started JQNZ in the first place?
And yes, it is no secret that AIPA is on the phone to NZALPA.