I can only speak from my experience with Eagle industrial actions. The first step was a call-out ban, followed by a full strike which thankfully didn't go ahead. The reason for this was pretty funny actually - the courier company, who assured the union that the strike notice would be issued on time, delivered late, making the strike illegal. Thankfully an acceptable contract was reached and the whole process worked as it's supposed to.
From my limited knowledge of goings on at Mount Cook, management are not playing ball with the new contract, and the Union is standing their ground. There is concern about their future, with Air Nelson operating the Q300 (and Air NZ holding options on more Q3/400s). I'm sure everything will work out, and wish them all the best. As the most profitable part of Air NZ, they do hold significant negotiating power.