The Serious Fraud Office is rejecting allegations it exceeded its powers by submitting evidence to Parliament's Privileges Committee.
The SFO entered the committee's highly-charged inquiry into a $100,000 donation from Owen Glenn which was used to pay lawyer Brian Henry, who works for New Zealand First leader Winston Peters.
The SFO is holding its own inquiry into other donations, and Peters has accused it of acting with malice and breaching section 39 of the Serious Fraud Act.
"What they've done is totally ultra vires (beyond its powers) and they've done it with malice in my view and I will set out to prove it," Peters told reporters.
Section 39 of the Act requires the SFO "to observe the strictest secrecy in relation to any information which is protected under any Act other than the Inland Revenue Department Act".
But SFO director Grant Liddell says he rejects any suggestion there has been a misuse of statutory powers.
"I reject claims that there is any impropriety, improper purpose or bias in my decision," he says.
NZPA understands the SFO sought advice from the Clerk of Parliament and the Auditor-General before it submitted evidence to the committee.
The evidence, which was considered by the committee during a closed session on Thursday, is understood to relate to $40,000 in court costs Peters was ordered to pay National MP Bob Clarkson after a failed electoral petition after the 2005 election.
Henry has told the committee he paid the $40,000 and then Peters paid him back.
Peters, an old foe of the SFO, has produced a letter written to one of his MPs, Ron Mark, by an anonymous SFO staff member attacking NZ First because it voted for a bill that abolishes the office and merges it with the police.
"The SFO will not find a thing in relation to NZ First's accounts," Peters says.
"That's why they've sneaked along here."
The committee has to decide whether the $100,000 donation should have been declared to electoral authorities.
Glenn has said Peters asked for it in December 2005 but the NZ First leader denies knowing anything about it until July 18 this year.
The committee has to report to Parliament by next Tuesday.
