A second strike notice has been filed on behalf of hundreds of St John paramedics and ambulance staff who plan on walking off the job next week.
St John staff represented by First Union say further breakdowns in pay talks mean they will now be striking next Wednesday and next Saturday.
First Union national ambulance co-ordinator Sarah Stone said negotiations with St John were not progressing.
St John was refusing to "move at all on what's written into an agreement - written into the collective contract.
"Ambulance officers who are members of FIRST Union all over the country are just so angry and upset with their employer that they don't see another way forward."
The two 24-hour strikes will now take place on 25 and 28 November.
Stone said it was a last resort over repeated denials from St John to honour a deal to pay the 1.25 penal rate pay it agreed to following low level industrial action by St John staff last year, but said it could no longer afford.
"Let's be absolutely clear about this - FIRST Union ambulance officers don't want to have to go on strike, they want to go to work and they want to be paid for the hours that they work. That's all they want."
But St John said its $60 million pay settlement over two years was the biggest in its history - and paramedics and ambulance officers appeared to be split over accepting it.
Pay settlement 'unprecedented'
Two other unions representing St John staff - the New Zealand Ambulance Association (NZAA) and the Amalgamated Workers Union of New Zealand - are recommending their members take it.
NZAA employment relations advocate Mark Quin said the deal offered one off settlement rates for all staff, a penal rate of time plus 15 percent for weekend and shift work and payrises from 10 percent through to 21.5 percent over two years.
"Considering in this economic climate, I would say that's unprecedented in any other industry at the moment."
The offer brought paramedics pay in line with overseas ambulance services and addressed pay issues faced by lower qualified ambulance officers, Quin said.
"Members who are sitting currently on $45,000, are actually going up with penal rates and base pay, to $60,000.
"That is quite significant - particularly with young families and trying to buy houses, that's the difference between being able to do that and not."
But Stone disagreed - she said staff represented by those unions were typically at the higher end of the scale and not everyone stood to benefit in the same way.
She said FIRST Union was pushing for the higher penal rates agreed to last year, as well as guarantees around rostering and the reduction in pay of some communication centre staff.
In a statement, the Ministry of Health said St John was in collective bargaining with three unions - with one union set to take strike action.
It said there would be a government contribution to settlement costs, however, the amount and conditions were yet to be finalised, and government officials would continue to support ongoing discussions between the parties.
St John hopes to reach agreement
St John deputy chief executive Sue Steen said it continued to work in good faith with all three unions and hoped to reach an agreement that met the needs of all parties.
"St John would like to reiterate that it has made a significant and unconditional offer to its unions which delivers on St John's commitment to improve the pay of frontline ambulance staff by implementing the full findings of an independent remuneration review."
She said St John was working on a contingency plan with FIRST union to ensure a safe service to the public during the withdrawal of labour.