The Serious Fraud Office says it found no evidence of criminal conduct relating to donations made to Christchurch mayor Lianne Dalziel and has closed its investigation.
Last year the Christchurch City Council's electoral officer was asked to investigate why Dalziel failed to identify donors who made contributions to her campaign.
An auction run by Dalziel's husband, Rob Davidson, brought in $40,000, but she did not declare the individual contribution.
The Electoral Act requires donors of sums greater than $1500 to be identified.
After public pressure she revealed the names of six donors from the auction who gave more than $1500 including one which totalled $17,850 from a person named Wei Min Lu.
The other donors who gave above $1500 in the auction were Yong Chen ($3920), Zhe Cheng Tan ($2800), Jiang Ping Wang ($2350), Grandland Investment Ltd ($2950) and Yang Xia Wu ($1750).
The shareholders of Grandland Investment are Chen Bing and Shi Shaohuan.
At the time Dalziel assured ratepaters she would not be influenced by Chinese donors.
In February this year the Serious Fraud Office received a referral from police over Dalziel's election expenses.
Serious Fraud Office director Julie Read, said it was the public interest that allegations of electoral funding fraud be treated seriously and given due attention.
"In a representative democracy, voters must have confidence that those who make electoral donations do not unduly influence government decisions.
"While there was no evidence of corrupt conduct in this matter, the SFO believes further guidance is required at the local government level relating to donations made at fundraising auctions and how they are publicly disclosed," Read said.
In a statement, Dalziel welcomed the SFO announcement.
"I was always confident in my case however they are required to investigate any complaint they receive thoroughly and they have done so. I am grateful they were able to clear the air before what will be a difficult Christmas for me.
"I agree with the SFO that further guidance is required relating to donations made at fundraising auctions and how they are publicly disclosed, and I would support a law change to provide for that.
"I will be making no further comment."
Rob Davidson, Dalziel's husband, died earlier this year at the age of 69 after suffering from cancer.
John Minto, who campaigned against Dalziel for the mayoralty last year, received an email this morning stating the investigation had been closed.
Minto said the decision not to prosecute Lianne Dalziel was a disappointing outcome.
"It sends a message that candidates might as well not even bother sending in an expenses return if this is the regard which the SFO has of this.
"The law says even if you inadvertently send in an incorrect expenses return than that is a breach of the law.
"The Serious Fraud Office are sort of ignoring the fact it breaches the law and saying that intent is the issue here."
Lobby group Keep Our Assets Canterbury said it was deeply disappointed the Serious Fraud Office had ended its investigation.
Keep Our Assets spokesperson Murray Horton said Dalziel's explanation of her failure to disclose donors to her 2019 campaign was not credible.
Ratepayers also still did not know the identities of the donors to her 2016 campaign, which she should release in good faith, Horton said.