Conservation Minister Maggie Barry is "disappointed and deeply saddened" by the killing of four endangered takahe.
The birds were shot during an organised pukeko cull on Motutapu Island, north of Auckland, earlier this week.
Ms Barrie says she's been fully briefed by her department but can't comment further because there's an investigation underway.
Labour's conservation spokeswoman, Ruth Dyson, says she expects a full explanation from the minister.
"There are only 263 of these unique birds left on the planet," she said.
"It beggars belief that four endangered takahe were killed by incompetent cullers contracted to the department."
Ms Dyson says it appears the culling was completely unsupervised, given the dead takahe were found some time after they were shot.
The birds' deaths have led the Department of Conservation (DOC) to immediately end its pukeko cull until an investigation is completed.
The Deerstalkers' Association has already apologised after four of the protected birds were shot and killed during an organised cull this week.
President Bill O'Leary said a DOC investigation would prove one or more of his association's members killed the birds during a hunt on Motutapu Island, north of Auckland.
"I share with the department a concern that the deaths will affect efforts to save an endangered species," Mr O'Leary said in a statement.
"I apologise to the department and to the country at large.
"I trust that this tragic incident will not harm the generally positive relationship we have with the Department of Conservation."
DOC yesterday said it would halt the cull while it conducted its investigation.
Northern conservation services director Andrew Baucke said it was particularly disappointing because the department had carefully briefed hunters on the difference between takahe and pukeko.
Those guidelines were introduced seven years ago following the shooting of a takahe on Mana Island, he said.
Motutapu Restoration Trust founder Christine Fletcher called the killings "completely unacceptable".
"It's devastating for those of us who've worked for 21 years to bring this about and that we can have lost four of these precious, precious taonga in one day. It's repugnant to me, so we will be looking for accountability," she told Radio New Zealand.
"We will be seeking, obviously, from the Department of Conservation some real explanation for what has happened."
The flightless takahe, once thought to be extinct, is classified as critically endangered.
The takahe is distantly related to pukeko, leading to its similar looks and characteristics.
Takahe and pukeko, not quite birds of a feather. Can you tell the difference?