Labour is laying a breach of privilege complaint against Prime Minister John Key, claiming he misled parliament.
If it was proved Mr Key deliberately misled parliament he would have to resign.
It's over comments Mr Key made on May 26 about the government's decision, announced in the May 21 budget, that the KiwiSaver $1000 kick start payment was being scrapped.
Labour's Grant Robertson today released details of the exchanges in parliament on May 26:
Mr Key: "The removal of the $1000 kick start contribution will not make a blind bit of difference to the number of people who join KiwiSaver."
Metiria Turei: "What evidence does the prime minister have that the sign-up rates for KiwiSaver will not be affected?"
Mr Key: "That is the formal advice from the Inland Revenue Department... I would be very, very surprised if it changes at all as a result of this."
Mr Robertson says Treasury documents released yesterday show IRD's advice to the government was the opposite.
"Inland Revenue actually said the impact of scrapping the kick start on KiwiSaver providers would be `a lower number of KiwiSaver members (particularly among the self-employed and children)'," Mr Robertson said.
"Instead of reflecting this advice, the prime minister made a blanket statement claiming the IRD backed his position.
"The prime minister has a fundamental requirement to tell the truth to parliament."
Mr Robertson will send his complaint to Speaker David Carter.
'There is now a pattern of behaviour from him, in terms of coming to parliament, making statements that are then not backed up by official advice," Mr Robinson told RadioLive.
"He'll no doubt find some weasel words somewhere in a paper he thinks will justify this."
Mr Carter will decide whether the privileges committee, which sits as parliament's court, should hold an inquiry and pass judgment on it.
He won't announce his decision until parliament sits again on July 21.