The New Zealand Nurses Organisation is calling for a nurse-to-patient ratio to be legislated.
A conference focusing on nurse-to-patient ratios opened on Tuesday in Wellington.
NZNO president Anne Daniels said the union has been calling for this legislation since 2001.
"We have actually seen it get worse over those 23 years," she said.
And kaiwhakahaere Kerri Nuku said they have seen an erosion of resourcing into the health system.
"What we've seen is that nurses have come under incredible pressure to perform more with less and at some point we see that it impacts on the quality of care that we can deliver to any patient," she said.
In October, more than 150 doctors, nurses and healthcare assistants at Auckland City Hospital signed a complaint to management, and lodged it under the Health and Safety at Work Act, warning hospital bosses that "safe staffing levels" were being "consistently breached".
Health Minister Dr Shane Reti said the coalition government had made recruiting more nurses a priority since coming into power.
He said Te Whatu Ora now employed more nurses than ever before, with a total of 29,404 full-time equivalent nurses.
"In the last three months alone, Health New Zealand added 1198 full-time equivalent to our health workforce," he said.
But Daniels said it was not just about increasing the number of nurses, but having enough with the right expertise, experience and skill to match patient needs.
She said the union had been trying to implement a Care Capacity Demand Programme, which would do exactly that, but had not been put in place despite "fairly numerous agreements".
"We can no longer depend on the government and nurse employers doing the right thing by us, because they clearly haven't for over 23 years, so now we have to move forward and have some certainty in the legislation."
