Waikato District Health Board risks losing its ability to train first-year doctors, after failing an accreditation review.
District health boards (DHBs) require Medical Council accreditation to train doctors in their first and second years of practice.
A paper presented to a board meeting earlier this week shows the Medical Council's draft report failed the DHB on four out of 22 standards, including medical workload issues and intern welfare.
The issue was being treated as "a matter of urgency", the paper said.
The final report had now confirmed those findings, a DHB spokeswoman told RNZ.
Tanya Maloney, who is chairing a steering group working to get accreditation back, said the DHB had been granted an extension of its accreditation until March, by which time she was confident it would pass all the standards.
Resident Doctors Association national secretary, Deborah Powell, said the loss of accreditation was deeply worrying.
"It's huge - if you can't meet the standards for first-year house surgeons, it pretty much sends shivers down your spine.
'It's serious... it's a very serious sign that something is not well in the hospital at all."
Some of the problems came down to being understaffed.
"The council was concerned that the workload wasn't consistent with good patient care, or a safe working environment, they were also concerned there was insufficient cover for the medical patients on night shifts for instance."
Dr Powell said the DHB was short of about 30 resident doctors.
Ms Maloney said it was unusual but not unique to fail the Medical Council standards.
"My understanding is that a number of DHBs have failed to meet some standards as we have. I'm not saying we're happy with the situation because we would strive to meet all of the standards.
"It would be unusual to lose accreditation - I don't believe it has happened before."
The DHB was already addressing the failures.
"We've had approval to recruit an additional three education supervisors and we're recruiting to that right now.
"The workload issues we are beginning to address. We've made job offers to two additional house surgeons and that will allow us to put another one on in medicine at night."
The DHB was not understaffed, she said.
"But what we do need to do is make sure we have additional doctors ... that allow the doctors on the floor to take leave and access to leave has been a problem."