The union representing the majority of ambulance staff says industrial action will continue despite four other unions reaching a collective employment agreement with St John.

First Union spokeswoman Lynette Blacklaws said the agreement wasn't one that its members would support, so their position hadn't changed.

First Union represents about 850 ambulance officers, who are protesting because they say they are overworked and do not get mandated rest breaks, which leads to fatigue.

They are having a uniform strike on Friday, when they will still respond to emergencies, but will wear T-shirts with the words "Healthy Ambos Save Lives".

The unions that have reached agreement with St John are the Amalgamated Workers Union NZ Southern, Central Amalgamated Workers Union , NZ Ambulance Association and Ambulance Officers Workplace Union.

The agreement includes annual pay increases of between 1.25 percent and at least 1.7 percent over the next three years, extended alternative days leave allocations and new meal break provisions.

The deal, which followed seven months of negotiations, still has to be ratified by members.