The Electoral Commission has ruled that there was no offence committed by New Zealand First's secretary in relation to the party's 2007 annual return of donations.
But in a summary of a withheld decision, the commission said donations made to the party in 2005, 2006 and 2007 were not included in New Zealand First's returns of donations.
The party has already updated its 2007 return and is now required to do the same for the two other years.
Two weeks ago, the Serious Fraud Office cleared the party of any fraud charges relating to donations channelled through the Spencer Trust.
At the time, it referred information to the Electoral Commission and to police.
The commission says it is withholding the full decision for now to avoid potential prejudice to the continuing police investigation.
The commission also found the ACT Party should have disclosed it was provided with rent-free office space by Sir Robert Jones for a number of years before 2005.