The Prime Minister is being accused of threatening the safety of four SAS logistics officers in Afghanistan to gather intelligence, by speaking publicly about the operation.
John Key told the media on Thursday the non-combat officers are there to build a case on insurgents responsible for the death of five New Zealand soldiers last month.
He says information will be handed over to the United States military's special forces, so they can find those responsible for the killings.
Mr Key says it is unlikely that SAS combat troops would also be sent.
The Labour Party's former Defence Minister, Phil Goff, says the prime minister has tipped off the intelligence officers' Taliban enemies and threatened the security of all New Zealand soldiers serving there.
"By big-noting in the way that he has, the Prime Minister has effectively put in jeopardy the lives of the four New Zealanders that he sent up there. That would never have happened in the past; I can't understand why he would have made a comment like that in advance of any operation."
However, defence analyst Jim Veitch says the Taliban will already be aware of the situation.
And he says the intelligence mission is also about preparing for the safe withdrawal of all New Zealand soldiers next year.
Mr Key says he has not been given an assurance from the United States that a retribution attack would be carried out on those responsible for the deaths of the New Zealand soldiers in Bamyan province.
"In the event that we can build that case, because you have to go through quite a legal process, then that would allow essentially an action to be taken against those people.
"That would be almost certainly undertaken by American special forces."