The Professional Firefighters' Union said low wages and "crisis level" staffing ratios are behind planned strike action.
Firefighters have rejected an offer to settle their collective agreement and voted to down tools.
Dates for any strike action are yet to be decided and could take several forms, union national secretary Wattie Watson told RNZ.
The union had asked for an 18 percent pay rise over three years.
She said under the Fire and Emergency NZ offer, the bulk of members (more than two thirds) would receive a 1.5 percent pay rise lasting for two years. They have not received any increase since 1 July 2020.
FENZ had made a "decent" offer for recruits and the first level of firefighters but there remained several other wage issues where the two parties disagreed.
Auckland Union committee member Terry Bird who is also a firefighter is among those supporting industrial action.
Every fire appliance has at least four staff and if people are absent for whatever reason they must be replaced - meaning shift workers like him can do 70 to 80 hours a week, he told Morning Report.
Bird said firefighters work hard to provide the community with services but it can be exhausting.
"I could work more hours and I choose not to. I need to get some rest, I know that I need to catch up on sleep."
Firefighters often had to deal with members of the public when they were facing a tragedy and it was hard to cope when they were tired because of staffing pressures.
He said firefighters had been enduring staff shortages for years, especially at weekends and holidays.
He had reviewed a collective agreement from 2018 in which both FENZ and the union recognised the problem of staffing levels in Auckland.
A commitment was made to set up a task force to address the problem.
"This is not new to FENZ but in the meantime, they've done nothing," Bird said.
Fire and Emergency NZ chief executive Kerry Gregory has accused the union of using "alarmist language" around staffing levels being the same as in 1980.
There had been variations in staff numbers since 1980 but staffing was sufficient to serve communities.
"We've got enough staff to ensure that we provide the service that we need to New Zealand," he told Morning Report yesterday.
He also said the pay offer from FENZ was "fair" and provided an overall increase for staff of 3.3 percent.
It was split up, meaning some junior firefighters would receive an 11 percent pay rise while the two grades above the juniors would receive a 7.5 percent increase.
RNZ
