About 1000 St John ambulance staff striking over better pay and staffing levels will from tomorrow refuse to go off the front line to cover commercial events.
First Union members are striking for a better pay rate that recognises the unsociable and physically tolling around-the-clock rosters they are on.
The strike action comes after mediation talks between the union and St John stalled last week.
By only refusing to attend non-emergency event work, the union was confident patient safety would not be put at risk.
First Union Transport, Logistics and Manufacturing Secretary Jared Abbott said St John needs to be reminded of its operational obligations to everyday New Zealanders.