When the Jetstar NZ pilots filed a strike notice quite a bit of NZALPA money was spent on obtaining a legal opinion from a QC with regard to this exact scenario. The general theme of it was that if you can show that Aussie pilots were being imported to carry out work that would normally be flown by NZ crews then an injunction to stop this would likely be successful. The onus would be on Virgin NZ pilots though to prove what flights they crew or what percentage of their work is crewed by NZ pilots as opposed to AUS crew. It is highly complicated and the AUS crews are under NO obligation to turn down work to keep the flights going (except maybe morally), it would be entirely up to NZALPA and the Virgin NZ pilots to stop them.