Up to 17,000 hospital support workers are being balloted from today on strike action.
The dispute centres on the implementation of a job evaluation scheme.
Health Care Assistants, chefs and other support grades will vote on industrial action over the coming weeks.
Siptu Health Division Organiser Paul Bell says other workers are also becoming involved in the row:
Mr Bell said: "The strike ballot will take place in 36 acute hospitals throughout the State, commencing today and concluding on May 17th.
"There are other workers who have now become involved in this matter because they would see that the Government have tried to renege on an agreement which is an integral part of the Lansdowne Road Agreement, which they supported in a secret ballot."