Len Brown's mayoral campaign says most of the anonymous donors who helped fund his successful bid to be Mayor of Auckland requested privacy.
Mr Brown spent $580,000 to win the race; almost $500,000 of that was contributed anonymously through a trust.
A campaign spokesperson told Radio New Zealand that most donors want their contributions to be private, simply because they are private citizens with no interest in being in the media.
Second-placed candidate John Banks spent almost $950,000, with $500,000 donated anonymously. Colin Craig, who finished third, spent $570,000 of his own money.
Local Government minister Rodney Hide says Parliament's Justice And Electoral Select Committee will look anonymous donations during a review of the recent elections.
At the moment, he says local elections differ in that regard from general elections and the question will be whether the rules should be the same for both.