Nurses and midwives at every major hospital in NSW will be walking off the job on 24 July.
Staff at nearly 180 public hospitals and community health services across the state have notified the union about their plans to strike. They are protesting over the state government's failure to provide safe nurse staffing levels.
NSW Nurses and Midwives' Association General Secretary Brett Holmes said more branches were expected to join the cause.
"For a few hundred million dollars a year the state government can dramatically improve patient care in our public hospitals," he said in a statement on Sunday.
The union campaign message is "Ratios put patient safety first." The union is calling for an increase in the number of nurses per patient, to bring a greater level of stability and reliability to the health system and improve patient experiences and outcomes.
They are calling for one nurse to four patients in all general medical, surgical and acute inpatient mental health wards; one nurse per three children in general children's wards and one nurse to three patients in emergency departments.
The extra staffing would "save lives and money", says Brett Holmes, adding that the nurse-to-patient ratios needed to be consistent at every hospital in NSW, including those in the country.
A special general meeting will be held at Sydney Olympic Park Sports Centre from 11.30am (AEST) on the day of the strike, with a live webcast to 17 regional centres, including Albury, Broken Hill, Kempsey, Tamworth and Wagga Wagga.
During the strike, life-preserving services will be maintained in all hospitals and community health services.