The National Ambulance Service, operated by the HSE, has said detailed contingency plans have been put in place for tomorrow's strike of around 500 ambulance personnel belonging to the Psychiatric Nurses Association.
Pickets will be placed at a number of venues across the country between 7am and 5pm.
A spokesperson for the PNA said their members would only operate services for "life-threatening or potentially life-threatening" calls.
According to the HSE, SIPTU has confirmed that it expects its members to work as normal tomorrow.
Managers who are qualified paramedics will be carrying out front-line duties, while the Department of Defence has made a number of crewed ambulances available for tomorrow.
The dispute centres on the HSE's refusal to recognise the PNA - and their ambulance personnel's branch NASRA - as representatives of the staff in question.
The HSE said in a statement, "Recognising break-away unions has a destabilising effect on good industrial relations."
The HSE has also refused to deduct and remit union subscriptions through the payroll system as it does for employees belonging to other unions.
The PNA spokesperson said the ambulance members were determined to uphold their eighth to he represented by the union of their choice.
SIPTU which represents around 1,300 of the 1,800 ambulance personnel is not in dispute with the HSE.
Additional reporting Sharon Tobin