Tens of millions of dollars have been incorrectly paid out to beneficiaries since 1993 because of an automatic payment mistake at the Ministry of Social Development.
Almost 90,000 beneficiaries have been affected by the error, which resulted in thousands of people being given incorrect accommodation supplement payments across 21 years, according to RNZ.
It is believed more than 41,000 people have been underpaid a total of $23 million, and just under 46,000 people have overpayments of about $32 million.
The mistake was discovered in September 2014 and was fixed a few months later, but Social Development Minister Anne Tolley was not informed until March this year.
Speaking to reporters at Parliament this morning, Ms Tolley said she did not know why she was not told about the mistake until 18 months after it was detected.