ACT Party leader Rodney Hide predicts the Serious Fraud Office will take months to investigate donations made to New Zealand First and its leader, Winston Peters.
The investigation covers money donated by businessman Sir Robert Jones and the racing industry's Vela family.
Mr Peters' lawyer, Peter Williams QC, says he gave the SFO documents on Saturday that will clear the New Zealand First leader of wrongdoing.
But, Mr Hide who complained to the SFO about the donations, says the investigation will hang over the election.
He says the nature of the complaint means it will take more than five minutes to resolve.
The Serious Fraud Office announced on Thursday it will look into accusations that donations to New Zealand First from Sir Robert and the Vela family did not reach their intended destination.
In addition, the Privileges Committee has invited Mr Peters, Brian Henry QC and expatriate businessman Owen Glenn to give evidence next Thursday.
The committee is considering whether Mr Peters should have declared a $100,000 donation from Mr Glenn towards legal bills in 2005.
Prime Minister Helen Clark revealed on Thursday that Mr Glenn told her in February that the New Zealand First leader had approached him for money.
Meanwhile, the Labour Party says Owen Glenn turned down a request to contribute further to the party.
Mr Glenn is Labour's biggest donor, giving the party $500,000 before the last election.
Labour Party president Mike Williams says he sought further contributions from Mr Glenn in July while on an overseas fundraising trip.
Mr Williams says although Mr Glenn declined his request, he told him he will consider donating to Labour in the future.