Auckland City Council staff say their privacy was breached after auditors checked a million emails during an investigation into Mayor Len Brown's an extra-marital affair with Bevan Chuang.

The council has told the staff members if they were concerned about the review, they should make a formal complaint, Radio New Zealand has reported.

The concerns related to the scale of the investigation and staff in the mayoral office were not told of their involvement in the review.

In a statement to RNZ the council said it had a "robust and best practice IT policy'' which had been agreed to by the users.

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In this case it struck a balance between its statutory and public sector roles and this was an investigation into whether there was misuse of public money, the council said.

The council said it would not review the inquiry.