The action will see members engaging in a campaign of non-cooperation with work outside of responding to emergency calls
Retained firefighters have begun a campaign of industrial action.
Their union SIPTU has accused the Government of failing to address a worsening recruitment and retention crisis in the service.
Members of the retained service are part-time firefighters who are paid an annual retainer to be available for call-outs.
The industrial action, which begins today, will see members engaging in a campaign of non-cooperation with work outside of responding to emergency calls.
This will involve refusing to engage in training exercises and drills.
It will also see radio calls through the emergency centres being replaced by the use of mobile calls to fire service management.
If there is no resolution to the dispute, rolling strikes will begin from 13 June which will see a series of one-day work stoppages at 50% of fire stations at any given time.
If there is still no resolution, an all-out strike will begin on 20 June.
In January, SIPTU members in retained fire service voted overwhelmingly in favour of industrial action.
The union said that many firefighters are unable to take their leave entitlements due to staff shortages and have seen their incomes drastically reduced due to reductions in call outs over the last number of years.