The Nurses Organisation says hospital patients are soiling themselves because there aren't enough nurses to help them to the bathroom.
The group, which represents more than 46,000 people, says it's the direct result of an almost $2 billion funding shortfall in the healthcare sector.
Spokeswoman Carol Beaumont it's not fair for patients or their nurses, who are feeling guilty about having to ration care.
"Nurses and healthcare assistants are there because they want to care for the needs of the people in the health system," she told Newshub.
"They are being stopped from doing so because of short-staffing."
Ms Beaumont, a former Labour MP, says funding and staffing are tight across all district health boards, but especially so in Auckland.
The $1.85 billion figure comes from the Council of Trade Unions (CTU), which says funding hasn't kept up with inflation and the country's ageing population.
"That is a systemic underfunding," says Ms Beaumont, claiming some aged care staff are bringing in extra supplies – such as incontinence pads.
The health sector received a record boost in last year's Budget, but an editorial published in the New Zealand Medical Journal around the same time concluded health spending was sliding backwards - falling in proportion to GDP.
A study published earlier this month, also in the New Zealand Medical Journal, found one-in-six Kiwis are skipping doctor's visits because they cost too much.
Newshub has reached out to Health Minister Jonathan Coleman for a response.