It follows a series of recommendations by the Labour Court.
On-call firefighters are to strike for a second time in two months over pay and conditions in the service.
SIPTU says members have voted to reject Labour Court recommendations supposedly offering "an interim solution" to their dispute.
The union says stations across the country have "dangerously low levels of crew on call out".
Previously suspended strike action is set to resume next Wednesday.
Retained Firefighter in Mullingar, Tony Sheeran, says the recommendations put forward by the Labour Court were 'way off' what they were looking for:
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