There is a warning about major staffing problems at the centre which takes calls and dispatches ambulances across the country.
SIPTU has written to the National Ambulance Service, claiming the National Emergency Operations Centre has fallen below the agreed staffing level by 35 workers.
The centre operates across two sites in Tallaght in Dublin and in Ballyshannon in County Donegal.
SIPTU Organiser, John McCamley, says a similar shortfall in 2016 led to a strike at the Dublin base.
He said: "There's now 35 permanent vacancies within the National Ambulance Centre. Around two years ago, the same level of permanent deficit lead to a dispute at the Tallaght centre.
"We had arranged an agreement to bring the staffing levels up, but unfortunately elements of that agreement have not been implemented by management."