Prime Minister John Key is challenging the New Zealand First leader to repeat allegations, without the protection of parliamentary privilege, over the leaking of a highly sensitive report into the Government's electronic spy agency.
A report into illegal spying by the Government Communications Security Bureau (GCSB) was leaked to Fairfax Media in April this year.
During a select committee hearing on Wednesday, Winston Peters accused Revenue Minister Peter Dunne of leaking the report to the media.
Mr Dunne flatly denies any involvement in the leak and, outside the Parliamentary committee where the accusation was made, he described Mr Peters's tactics as a scurrilous stunt.
John Key said he takes Mr Dunne at his word and that if Mr Peters is serious, he should repeat his claims without the protection of privilege.
Mr Peters said it is his right to protect himself against legal action while carrying out his duties as an MP.
During Question Time in Parliament on Thursday, the Labour Party raised questions about why Peter Dunne was the only minister to be questioned by David Henry, who is leading the inquiry into the leak.
Speaking from Timaru, John Key said there is nothing sinister in that and is also sceptical that the report will reveal who it was.
Mr Key said there are so many opportunities for people leak documents without leaving what he calls fingerprints.
The result of the inquiry into who leaked the report is due to go to the heads of the Department of Prime Minister and Cabinet, and the GCSB on Friday.