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The New Zealand Professional Firefighters Union plans to take one-hour strike action on August 19 and 29.
Fire and Emergency New Zealand has been advised union members will stop work from 11am to noon on those days, and includes all career fire stations, training centres and 111 fire communications centres.
"This is an unprecedented step that has not been taken lightly but reflects the gravity of the situation," the union said in a statement last night.
The union also wrote to Fenz seeking mediation talks next Wednesday and Thursday in a bid to get discussions moving towards reaching an agreement.
During the strikes, Fenz will continue to respond to emergencies.
However, areas served primarily by career firefighters may face longer waits than usual.
Union claims centre on safe systems of work and safety, health and wellbeing.
Fire and Emergency Deputy National Commander Brendan Nally said it was disappointing the union had given notice of escalated strike action, despite a "substantial new pay offer" which would see base salaries for all firefighters increase by between 8 and 19% over the next two years.
"The NZPFU has notified us their members will withdraw all labour for an hour between 11am and 12pm on two different days - on 19 August and 26 August. They have also indicated they wish to return to mediation but are yet to provide a counter position," Mr Nally said.