Nurses stepped up their campaign for a pay increase and a shorter working week with the first in a series of protests today at Cork University Hospital.
The General Secretary of the Irish Nurses Organisation, Liam Doran, told RTÉ Radio's News At One that a nationwide work-to-rule and short work stoppages may commence without further notice.
He called for their claims to be addressed immediately to avert further action.
Today's protest is the latest in a long campaign by nurses to improve their pay and conditions.
They are seeking a 10% pay rise, a further allowance for nurses working in Dublin, a reduction in the standard working week from 39 to 35 hours and the elimination of an anomaly under which qualified nurses and midwives are paid less than unqualified childcare workers who report to them.
Both the INO and the PNA say the Health Service Executive-Employers Agency failed to engage in substantive negotiations with them during the 21 days since they gave notice of industrial action.
The unions have planned further lunchtime protests for Limerick's Mid-Western Regional Hospital and Galway's University College Hospital on Friday.
However, in the meantime, they say they may engage in work stoppages or a nationwide work-to-rule with minimum notice to hospital managers.