The Irish Nurses and Midwives Organisation says it will ballot its members for industrial action unless pay and staffing levels are restored.
The union says its members cannot cope any longer with reduced salaries, unpaid additional hours and unsafe staffing levels.
It says the situation is unsustainable, unacceptable and dangerous.
INMO General Secretary Liam Doran says nurses feel broken and demoralised.
He said: "We are consulting with our members now in the next couple of weeks and we will ballot.
"That ballot, in the absence of proper staffing, will lead to the closure of beds and the curtailment of services, so that they match available staffing levels.
"Because otherwise our members are working in an unsafe environment and patients are being cared for with inadequate staffing that compromises their care."