The Ministry of Health says it will have to consult with a number of parties, including the Privacy Commissioner, before considering releasing data on Māori children who are eligible for the Covid-19 vaccine.
The vaccination roll-out for 5- to 11-year-olds started on Monday after Medsafe approved the Pfizer paediatric vaccine in December.
The Whānau Ora Commissioning Agency has said it plans to take legal action against the ministry to get it to release the data.
It comes after the agency took the ministry to court in 2021 for the contact details of Māori aged 12 and up who had not yet been immunised, so it could better target its vaccination efforts.
The agency's chief executive John Tamihere said immunising children was important for Māori, with one in four Māori under 12 years of age.
Ministry director of the national immunisation programme Astrid Koornneef said it had to date met all of its obligations to share Māori vaccination data with the agency in line with the December High Court ruling.
"While the decision provided very useful general guidance for the release of personal vaccination information about Māori, it did not consider the potential sharing of personal contact information and vaccination status about tamariki," she said.
"The information requested is sensitive, given it involves children's personal health and contact information."
Koornneef said the ministry would have to consult a number of stakeholders, including Māori, the Office of the Children's Commissioner and the Privacy Commissioner about sharing the information.
"The ministry has always been open to discussions with Whānau Ora, iwi, and other key groups about ways to strengthen the roll out of the vaccination programme to Māori, including the recently launched vaccination programme for 5-11 year olds."
Tamihere described the ministry's comments as typical stonewalling and said the agency's lawyers were preparing to file papers in the High Court.
"We're going to have to go to court and we're good to go."
Tamihere said if the agency had access to the data it would be able to text and email the families of Māori children who were eligible for the vaccine.
Whānau Ora providers, in areas like south Auckland, would then be able to target specific communities with large numbers of unvaccinated people.
Tamihere said the agency's ongoing legal battle with the Ministry of Health had already cost it about $450,000.