SIPTU said its members who are employed as retained firefighters will begin to resign from the service in large numbers from the beginning of next week as part of a dispute over pay and conditions.
Retained firefighters began rolling work stoppages on Tuesday which will be escalated to an all-out strike next week if the dispute is not resolved.
"There is no sign of a breakthrough in this dispute and with all out strike action to begin on Tuesday 20 June, which will result in the closure of all retained fire stations across the country, an increasing number of SIPTU members have made clear they are considering resigning from the service," said SIPTU Public Administration and Community Division Organiser, Karan O Loughlin.
"Many would rather walk away altogether. If this happens, with crewing already at crisis levels, the service will collapse and will take years to rebuild as those firefighters will not return if they leave," Ms O Loughlin said.
In a statement to the Dáil on Tuesday evening, Minister for Housing, Local Government and Heritage, Darragh O'Brien said he was committed to ensuring that the retainer payment received by part time firefighters will be positively dealt with in the upcoming public sector pay talks.
"I will be a strong advocate for and champion of firefighters on the retainer issue in the upcoming collective pay talks," Mr O'Brien said.
SIPTU said its members were "outraged" by the response and that it was nowhere near good enough.
Members of the retained service are part-time firefighters who are paid an annual retainer to be available for callouts.
SIPTU represents around 2,000 retained firefighters across 200 stations around the country.
The union said there is a recruitment and retention crisis in the service meaning that many firefighters are unable to take their leave entitlements due to staff shortages.
They have also seen their incomes drastically reduced due to reductions in call outs over the last number of years.
The issue was raised in the Dáil today and Minister O'Brien said that he was "confident" that it can be resolved.
The minister said that there was contact with the unions and the Government, and encouraged them to re-engage with the talks process.
He was responding to Sinn Féin's Pearse Doherty said that this is "really a crisis point" which "will result in the collapse of the service".
