The nurse's union says mistakes robbing nurses of tens of thousands of dollars are being made by the health systems pay back system.
Te Whatu Ora has paid back $250m of the almost $2 billion it owes to scores of thousands due to years of breaches of the overly complex Holidays Act.
But Nurses Organisation (NZNO) chief executive Paul Goulter said nurses were telling them of a range of mistakes in what they were getting, "from a few dollars to tens of thousands of dollars".
"We've been told that by nurses, we've also been told by some nurses they haven't received anything," Goulter said.
"So it looks like a real dog's breakfast.
"It's inaccurate and we can't trust its accuracy."
In a meeting on Wednesday, the health agency told them it was pulling back from issuing the rest of the tranches of the money, Goulter said.
"That's one of the reasons we understand why they've pulled back."
This meant yet more delays in nurses getting what they were owed, after waiting for years, and they would complain to new Health Minister Shane Reti, Goulter said.
Te Whatu Ora said the work "is taking longer than anticipated" but the work had not been paused and it did not believe there had been mistakes.
Chief people officer Andrew Slater said they were going as fast as they could to do the work once and get it right.
"We are confident in the accuracy of our Holidays Act remediation payments to date. These payments cover current employees for our seven payrolls in the Auckland region. A rigorous series of checks, testing and external assurance is involved before any payments are made.
"Not everyone is due to receive a payment - some people have had their leave paid correctly."
It took years for the unions and health authorities to agree on a formula and design for the payback system, across two dozen different hospital payroll systems and many years of mistakes in shift and annual leave calculations.
"We did arrive at ... the correct formulas for paying out, but still something else seems to have cropped up and they're not able to do it", despite the many costly consultants working on it, Goulter said.
"We're not sure why they can't do what they promised to."
As at December, 34,000 people had got paid, encompassing current staff in three districts in Auckland, Counties Manukau and Waitematā, and four shared, previous health services - Health Alliance, Health Partnerships, Health Source and Northern Region Alliance.
Another 17 districts, plus all former staff, were having to wait till this year for any pay back.
RNZ has approached Te Whatu Ora for fresh comment, after its statement on Thursday afternoon about its meeting with the NZNO did not refer to mistakes or any pause.
It said it was a big, complex job but it made a good start on paying people back last year.
"This work is taking longer than anticipated and we understand how frustrating that is, especially given this issue has been impacting our people for more than 10 years. We remain committed to complete remediation payments to our current employees in 2024."