Ambulance staff have voted in favour of industrial action.
SIPTU conducted a ballot in relation to their conditions of employment.
The union has said 92% of its members have backed action.
It says the Minister for Health and HSE are now on notice that they cannot guarantee ambulance services will not be disrupted or suspended during the period of industrial action.
SIPTU Health Division Organiser, Paul Bell said: “Unfortunately, our members have no option but to implement a campaign of industrial action.
"NAS management has also failed to adequately engage with our members concerning the implementation of a fully developed Intermediate Care Service, as recommended by the Labour Court, or in relation to the application of an annualised hours system”
“SIPTU organisers will now consult with our workplace representatives on what industrial action to implement with the aim of causing the least impact on the public.
"However, the Minister for Health and the HSE are now on notice that we cannot guarantee that certain ambulance services will not be disrupted or suspended during the period of industrial action.”