The Serious Fraud Office (SFO) is looking into Christchurch City Mayor Lianne Dalziel's election expenses.
In a statement, the SFO said the matter has been referred to the office by the police.
"The SFO will be assessing the matter and has no further comment at this time."
Newshub has contacted Dalziel for comment.
The Christchurch City Council's electoral officer had been 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 ran 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.
"I've been completely transparent, I actually have got nothing to hide, I never have had anything to hide, I relied on my husband's advice," Dalziel said in December, as reported by RNZ.
One of the people who asked the electoral officer to investigate was former mayoral candidate John Minto. He told Newshub on Friday he's pleased the concerns are being taken seriously.
"I think the public has a right to know who is funding these political campaigns," Minto said.