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.
Frontline emergency crews are concerned their services are being offered up to cover private hire for sporting and other commercial events run by private business - instead of emergencies which is what the majority of Government funding they received was for.
"St John is already being funded to provide emergency ambulance pre-hospital care, so should not be sending frontline staff to private events when we know we are short of ambulance professionals."
The union was also concerned that St John had rejected calls to approach the Government and lobby for a fully-funded service, rather than rely on volunteers and commercial activities.
"It is an indictment when you see an emergency health provider, unlike other frontline service providers, having to become beholden to commercial interests in preference to their contracted obligations."
Abbott said St John was already flying staff around the country to cover commercial events so thought the strike would mean event organisers would have to look to private companies who also provided ambulance cover for events.
St John director of people and capability Sue Steen said St John was in the middle of collective bargaining with its four unions and hoped to reach an agreement that suited all parties.
The organisation was also in close contact with its stakeholders and event customers during the strikes.
The strike will be ongoing until both parties reach an agreement.