The Serious Fraud Office has launched two separate investigations into donations made during both the Auckland and Christchurch mayoral elections.
A complaint was received by the SFO last month about donations from Christchurch mayor Lianne Dalziel's supporters during last year's mayoral race.
The SFO also received a police referral in relation to Auckland Mayor Phil Goff's election expenses.
At the time, Goff said he had no knowledge of any irregularities while Dalziel said she only heard about the complaint through the media.
The Christchurch City Council's electoral officer was asked in December to find out why Dalziel only identified six people who donated over $1500 to her mayoral campaign, Radio New Zealand reported.
They donated through an auction run by Dalziel's husband. Dalziel said she acted on her husband's advice, which was that donors who gave more than $1500 did not need to be declared. She later apologised.
In September 2019 a formal complaint was laid over Goff's 2016 election expenses declaration, relating to the declaration of cash donations from fundraising auctions of $366,115.
A spokesperson for Goff said the SFO is yet to contact them about the investigation.
"There has been no communication from the SFO about launching an investigation. They are yet to contact make contact with any details of an investigation.
We will not be making any further comment until we have been contacted about this."