Siptu members at Dublin Fire Brigade are to start industrial action on Monday, October 5, in protest over "critical" staffing levels.
They say Dublin City Council has failed to keep the minimum levels of staff to provide safe systems of work, with many firefighters doing "unsustainable" levels of overtime.
The industrial action will see workers refuse to do overtime on certain dates as a base level of action.
Siptu says Dublin Brigade is 70 firefighters under strength.
SIPTU sector organiser, Brendan O’Brien, said: “Further to the ongoing failure by Dublin City Council and the management of DFB to maintain agreed minimum safety critical staffing levels sufficient to provide safe systems of work our members have been left with no option but to commence industrial action.
“Initially, members will be directed to refrain from working unsustainable levels of voluntary overtime on selected dates.
“We will inform the management of DFB the dates that this action will be taken on in the coming days.”