Ambulance workers belonging to SIPTU and UNITE are taking industrial action today.
They're in a dispute with management because recommendations on their pay haven't been brought in.
Emergency Medical Technicians, Paramedics, Specialist Paramedics and Advanced Paramedics are among those involved in the action.
Today's work-to-rule will be followed by 24 hours of strike action tomorrow and a further two days the following week.
SIPTU Ambulance Sector Organiser John McCamley said, "Our members should be awarded enhanced payscales based on the work they've undertaken in the last 15 years in changing the service from primarily a patient transport service to a pre-[hospital] care service".
What does it mean for me?
The HSE has a contingency plan in place to prioritise patient safety and minimise disruption due to industrial action by the National Ambulance Service.
It says all other health services are operating as normal, and if there is any change to planned care the person will be contacted.
During the action, people should contact 999 or 112 if someone is experiencing a life-threatening illness or injury.
Priority will be given to patients facing cardiac or respiratory arrest, and those experiencing serious trauma from road crashes.
Dublin
In Dublin, the ambulance service is primarily operated by Dublin Fire Brigade, with some calls being given to the National Ambulance Service.
NAS covers certain parts of Dublin also - so these areas may be affected.
Dublin Fire Brigade haven't indicated yet if there will be disruptions - however their members are not on strike this week.
