Complaints to the Department of Conservation (DOC) have accused the Cape Sanctuary in Hawke's Bay of neglect.
It comes after Radio New Zealand revealed the complaints included concerns about high turnover of staff, the death of two kaka in cat traps in October 2017 and the death of nine Little Spotted kiwi in 2017.
Cape Sanctuary is situated on Cape Kidnappers, on three properties owned by American billionaire Julian Robertson, Andy Lowe and the Hansen family.
Music legend Sir Sir Paul McCartney made headlines last year at the sanctuary when he handled one of the kiwi, named Bubbalicious, who was reared at sanctuary.
Sir Paul's subsequent video was viewed more than 450,000 times and received more than 32,000 reactions.
The bird was one of nearly 200 to have been taken as an egg from Maungataniwha Native Forest as part of Forest Lifeforce Restoration Trust's (FLRT) Maungataniwha Kiwi Project which comes under the BNZ Operation Nest Egg initiative.
The sanctuary is the country's largest privately-owned and funded wildlife restoration project.
In March this year volunteers built a $700,000 aviary to help protect one of the nation's most endangered birds.
The survival of New Zealand's critically endangered shore plover (tuturuatu) is another step closer after the official opening of the sanctuary's Kotahi Aviary.
At the time, the sanctuary's co-founder Andy Lowe said: "It is fantastic to be part of a long-term partnership with the Department of Conservation and Kotahi to save a shore bird that will become extinct if we don't invest in active breeding and release programmes," Lowe said.
"It is our philosophy to develop long-standing partnerships with businesses, iwi and the Department of Conservation to restore native bird life for our future generations to experience native species in their natural habitat.
"In time, we will include New Zealand's iconic blue duck [whio] in the Kotahi Aviary. "The river beside the aviary provides a natural resource for this nationally vulnerable species that risks extinction with a population of less than 3000."