The Employment Court has thrown out a bid by Te Whatu Ora to stop a one hour strike at Gisborne Hospital's acute care unit on Wednesday.
The Nurses Organisation says the ruling upholds the vital right of workers to strike over health and safety concerns.
In a statement, its chief executive Paul Goulter said it was a moral victory.
"These Gisborne nurses have been raising concerns for more than nine months, and, as the judge pointed out during the hearing, Te Whatu Ora had not managed to change anything at all to help them. This is simply not good enough from one of the country's largest employers."
The union says exhausted nurses are working while sick and injured, and live with constant fear of making a fatal mistake.
Judge Kerry Smith said the Ward 5 strike encompassed health and safety concerns for the nurses as well as deep professional concern for patients.
Judge Smith said the hospital has had 14 days to make contingency plans to deal with the strike from 1.30pm to 2.30pm tomorrow.
Te Whatu Ora said it accepted that staff were under pressure - but was sticking to its argument that the strike would make things worse.
In a statement, its chief executive Fepulea'i Margie Apa said the hospital had two priorities - firstly, ensuring patients had the care they needed and secondly, working with the union to address the pressure on the hospital and its staff.