Labour MP Trevor Mallard has lodged an official complaint about Act leader John Banks failing to disclose a $15,000 donation was from SkyCity during his 2010 Auckland mayoralty campaign.
Mr Mallard lodged the complaint with the Auckland Council electoral officer this week. He also asked the electoral officer to scrutinise "anonymous" donations of radio advertising Mr Banks had included in his return.
SkyCity gave $15,000 each to Len Brown, now mayor, and Mr Banks, his rival, during that campaign.
Although Mr Brown's donation return listed SkyCity as a donor, Mr Banks' listed an anonymous donation of $15,000. It did not mention SkyCity.
The penalty for knowingly filing a false return is up to two years in prison or a fine of up to $10,000.
There is a lesser penalty of a $5000 fine if the candidate did not know it was false. MPs convicted of crimes with a penalty of two years or more can not remain in Parliament.
However, Mr Banks said he was not concerned about the complaint, dismissing it as Mr Mallard "up to his old timeless tricks".
He said he had not known at the time that the donation was from SkyCity and his donations return was accurate as at the date he signed it.
"I signed the document at the said time to the best of my knowledge."
Although SkyCity had subsequently publicly confirmed donations to both candidates he had not considered amending his return or asked further questions of his campaign team.
Asked how it was that Mayor Brown had known about the SkyCity donation yet he had not, the Act leader said his campaign accountants had dealt with the finances for his campaign and he had based his return on the information they gave him.
Asked if it was possible they had known the donation was from SkyCity, he said it was.
Auckland Council's electoral officer, Bruce Thomas, said he would consider the complaint and decide whether to refer it to police.