Siptu will begin balloting 1,200 emergency ambulance staff today for industrial action over a dispute with the Health Service Executive (HSE).
The threatened action comes after the HSE awarded contracts to three companies for the provision of a private ambulance service.
According to the HSE, the new service will be used to transport non-emergency patients between hospitals and other health facilities.
Unions disagree, saying it is the start of the privatisation of the 999 ambulance service. Siptu say a sub-committee made-up of both union and HSE personnel was put in place last year to discuss the introduction of a private service.
However the union says the contracts were awarded on December 27th without an agreement being in place.
The process of voting on industrial action begins today with a decision expected by February 22nd.