A National Party insider has told RNZ News that Simon Bridges amended his personal electoral donation return to remove two donations totalling $24,000.
The party leader's original return to the Electoral Commission, which he signed and dated on 17 January 2018, declared $120,000 of candidate donations.
In February, after the 23 January deadline had passed, Mr Bridges filed a new return with donations totalling $96,000.
A spokeswoman for Mr Bridges says the donations were incorrectly accounted for in his initial return and were transferred to the National Party and disclosed.
"As soon as this was picked up, the donations were transferred to the National Party and disclosed."
Mr Bridges' office wouldn't answer any questions about one of the donors - the Cathedral Club - and its $10,000 donation, directing questions to the party.
A spokesperson for the party declined to answer questions about the club but did attribute the donation error to the local Tauranga electoral committee.
"In the process of preparing both the local candidate and party returns, as required by the Electoral Act, two donations were incorrectly attributed to Mr Bridges' candidate return by the local Tauranga Electorate Committee,'' a National Party spokesman said.
"This error was discovered soon after lodging the candidate return, and the Electoral Commission was contacted immediately to seek advice.
"Acting on that advice Mr Bridges' candidate return was amended, and then re-submitted to the Electoral Commission for publication,'' he said.
It's understood the Cathedral Club is a new name for the former Cabinet Clubs where local business people host MPs and pay to hear about their politics.
A donation from Tauranga healthcare business, Cubro Limited, worth $14,000, was also reassigned from Mr Bridges to the party.
Mr Bridges' Facebook page shows a photo of him with Cubro Limited chief executive Logan Currie and company founder Lin Currie at the business in Tauranga in 2016.
The $14,000 donation was the largest Mr Bridges received up until its transfer to the party and the Cathedral Club donation was one of the second largest.
A spokesman for the Electoral Commission said they received more than 60 amended candidate returns for the 2017 general election.
The commission checks to ensure the candidate has signed and dated the declaration that the return filed is an accurate record of the candidate donations and election expenses and is not false.
Those processes were followed for Mr Bridges' return, a spokesman said.