An independent analyst says public auditors should have picked up an error with Christchurch City Council's rating policy.
Since 2004, formal rating resolutions passed by the concil have failed to include a reference to due dates and penalties.
Analyst Larry Mitchell said Audit New Zealand is supposed to make sure councils' rating policies comply with the law.
Mr Mitchell said the auditors are not paying enough attention to detail.
He said the council and Audit New Zealand are equally to blame for the error going unchecked for so long.
The Office of the Auditor-General is meeting acting city council chief executive Jane Parfitt on Friday.
The Department of Internal Affairs said on Wednesday the mistake was discovered by an analyst looking the council's regulations and it was notified on 22 July.
DLA Phillips Fox partner Craig Stevens said the problem seems to be limited to whether the council can impose penalties for late payments.
He told Morning Report the easiest fix is to introduce retrospective legislation to solve the problem.
Mr Stevens expects other councils will be looking at their own documents to make sure they have not made similar mistakes.