Opposition parties say United Future leader Peter Dunne cannot continue as an MP following his resignation as a government minister.
Mr Dunne resigned on Friday following an inquiry into the leaking of a highly sensitive report into the Government Communications Security Bureau (GCSB) in April.
Prime Minister John Key ordered the inquiry after Fairfax Media was shown a copy of Cabinet Secretary Rebecca Kitteridge's report on illegal surveillance and the current operations of the GCSB a week before Mr Key was due to release it.
The inquiry found communications between Mr Dunne and the journalist to whom the report was leaked that included references to the report's release.
Mr Dunne maintains he was not the source of the leak, but refused to release to the inquiry all 86 emails between himself and the reporter on the grounds of protecting individuals' privacy.
He will stay on as MP for the Wellington electorate of Ohariu and continue to cast his vote for the National-led government.
Labour leader David Shearer says it is untenable for Peter Dunne to continue as an MP under a cloud of suspicion. "He cannot come into Parliament as an MP with all the suspicion around him and not come forth with the evidence that would prove his innocence."
New Zealand First leader Winston Peters is asking for police to investigate and says Mr Dunne cannot stay in Parliament given the circumstances.
Green Party co-leader Russel Norman says the Prime Minister should ask police to determine who leaked the report, and says a police inquiry would have the power to force Mr Dunne to release his emails.
Former Labour Party president Mike Williams says Mr Dunne's political career is over and he should leave parliament quickly.
He says the leak of a highly-sensitive document is a very serious matter and if he were Mr Dunne's party president he would be telling him to go quietly.
However, former National Party president Michelle Boag says Mr Dunne has done nothing criminal and it would be a tragedy if his political career ends now.
She says the MP is guilty of a lapse of judgement but so have many ministers and MPs before him.
Government stable, says PM
Prime Minister John Key says Mr Dunne's resignation will not affect the National Party's ability to govern as it still has the support of ACT and the Maori Party.
Mr Key says he wants to believe Mr Dunne wasn't the source of the leak but because of his refusal to co-operate, can't rule it out.
He says Mr Dunne couldn't explain why he would not release all the emails so he told him he had to either comply or resign.
The prime minister says National will continue to work on policy matters with Mr Dunne but not in a ministerial role.
Mr Dunne says he has not decided yet whether he will stand again in the Ohariu electorate at the next election.