ACC Minister Judith Collins has asked for an urgent report into allegations that private details of thousands of ACC claimants were sent to an unauthorised recipient.
Some 9000 ACC claimants, including sexual abuse and rape victims, had their details emailed to someone who should not have received them, Fairfax Media reported.
The details include full names and the nature of individual's claims - including those of 250 people handled by the ACC's sensitive claims unit.
Ms Collins this morning asked ACC chief executive Ralph Stewart for a report into the matter.
ACC's senior managers were reportedly informed about the breach three months ago but made no effort to investigate or ensure the information went no further.
Before management was informed, former ACC Minister Nick Smith and the board were told about problems with the corporation's privacy processes.
A board member raised the issue at a higher board level, leading to a meeting between the email recipient and ACC management in December.
The allegations have sparked calls for an independent inquiry, with Green Party ACC spokesman Kevin Hague expressing particular concern about ACC's apparent lack of action.
"It appears the ACC board and the minister have known about the privacy breaches for some time but have done nothing about them,'' he said.
"We need to know what the board knew, what the minister knew, and why they have not acted. Only an independent investigation can achieve that.''
Mr Hague said there appeared to be a "lax privacy culture'' in the organisation, which undermined the trust New Zealanders needed to have in the scheme.
He noted that claimants who had had details about sensitive claims released would need support and possibly compensation.
A spokesperson said the ACC took all privacy complaints "extremely seriously", however there was no formal complaint.
Privacy Commissioner Marie Shroff told the Dominion Post the breach was likely one of New Zealand's most serious.