The Nurses Organisation is disputing staffing figures released by the Auckland District Health Board (DHB) in response to claims two of its hospitals are understaffed.
The union surveyed charge nurses at Auckland and Starship Hospitals and found the two hospitals were short of about 120 nurses.
In a statement, the DHB's acting chief executive Margaret Wilsher says there are more nurses on hospital wards now than there were last year.
She says 128 extra nurses have been recruited across both hospitals, including 28 extra staff for Starship Hospital.
But a union organiser Craig Muir says the DHB takes several months to fill positions and has stopped using casual and bureau nurses.
Mr Muir says every shift in every ward is down two nurses, and the shortage is compromising patient safety.
He says the DHB has told the union it's saving $50,000 a day, which suggests it's cutting staff.
An Auckland nurse says hospital staff shortages mean they can't do their jobs properly, and that is putting patients lives at risk.
A senior nurse, who does not wish to be named, says are two nurses down at each shift and have time to do only the very basic in care.
She says there have already been a few close calls and she believes it is only a matter of time before someone dies .