Around 500 ambulance personnel belonging to the Psychiatric Nurses Association are to strike on 19 December in a dispute over union recognition and the deduction of union subscriptions.
Staff around the country will stop work on that day between 7am and 5pm.
However, the remaining 1,300 workers in the ambulance service represented mainly by SIPTU are not in dispute and are expected to work normally.
Since 2010, the staff in question have joined a breakaway group called National Ambulance Service Representative Association (NASRA), which then affiliated to the PNA.
However, the Health Service Executive has refused to recognise the PNA/NASRA as having negotiating rights for the grades in question, which include paramedics, advanced paramedics and emergency medical technicians.
The PNA says the strike is in pursuit of its members right to be represented by the trade union of their choice.
They are also furious that the HSE has refused to process PNA/NASRA union subscriptions through payroll deductions in the way that it does for other unions.
Next month's strike will mark a significant escalation in this long-running dispute which has already seen the 500 staff working-to-rule since 10 October.
The National Ambulance Service (NAS) has said that both it and the HSE are satisfied that ambulance personnel are adequately represented through agreed industrial relations processes that exist in the health sector.
In a statement, the NAS said it has an ongoing engagement with SIPTU which is the recognised trade union for frontline NAS staff.
It said: "Recognition of other associations or unions would undermine the positive engagement with SIPTU, would impair good industrial relations in NAS and would not serve the best interests of its staff.
"This approach is in keeping within Government policy and supports the consolidation that is happening within the wider trade union environment."
"The principle of engaging only with recognised trade unions has been acknowledged previously by the Labour Court in a dispute involving the PNA and a different public-sector employer."
The NAS said the PNA's decision to take strike action "escalates an ongoing issue" and is being reviewed in line with existing policies and procedures.
It said: "The focus for the National Ambulance Service in all circumstances is to ensure service and care delivery is not compromised in any manner".
PNA General Secretary Peter Hughes said the dispute was entirely of the HSE's making and that his members had no option but to move to strike action in pursuit of the fundamental right to join the union of their choice.
He said the escalation to strike action indicated the strength of feeling among ambulance personnel.
The National Chairperson of the PNA's NASRA branch Sinead McGrath said it was outrageous for the HSE to continue to attempt to force ambulance personnel members of PNA into joining another union that they have made clear they do not want to be members of.
She said NASRA had successfully represented hundreds of members since its formation in 2010 and urged Minister for Health Simon Harris to instruct the HSE to stop its "pointless" efforts to frustrate the wishes of hundreds of ambulance staff.
