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:
Midlands Based Pharma CEO Picks Up Award
Six Months Of Traffic Disruption Ahead As Water Mains Works Begin In Westmeath
Hybrid Working Drives Irish Rail Services To Capacity In The Midlands
Young Musicians Set To Rock The Midlands At Youth Music Festival
Minister Rules Out Toll Reductions For Midlands Commuters
€7.5m Offaly Distribution Centre Development Set To Create Over 100 Jobs
Offaly Chocolatier Heartbroken As Factory Fire Halts Production
Drivers In The Midlands Urged To Take Responsiblity When Driving On Bad Roads