Labour and the Green parties oppose the return of New Zealand SAS troops to Afghanistan.
The Cabinet has approved three rotations of up to 70 SAS personnel over 18 months.
Their deployment was requested by the United States. SAS troops from New Zealand have previously been deployed three times in Afghanistan - the last time was in 2006.
Prime Minister John Key says New Zealand has a direct and vital interest in supporting international efforts to eradicate terrorism and to promote peace and stability in Afghanistan.
He says recent events in the Indonesian capital Jakarta, in which a New Zealander was killed in attacks on hotels, show New Zealand is not immune to terrorism.
Mr Key says deploying the SAS should ensure that Afghanistan government wrestles control of the country back from the Taliban.
He told Morning Report that Afganistan is an increasingly dangerous place and there is the possibility of fatalities.
Mr Key said sending the SAS will help New Zealand play its part in stabilising the country.
Complex conflict - Goff
Labour leader Phil Goff says the most effective way of helping in Afghanistan is to win the hearts and minds of the people.
Mr Goff told Morning Report it was right for Labour to deploy the SAS three times while in Government, but that is no longer the case.
He said al Qaeda was launching international terrorist attacks from a base in Afghanistan at the time.
Mr Goff said the war has changed significantly since then and it is now a more complex internal conflict between the Taliban and the government forces.
The Greens say the SAS should stay at home.
Withdrawal from Bamyan
A plan is also being drawn up for the withdrawal of a provincial reconstruction team from Bamyan over the next three to five years.
Instead, there will be a focus on providing civilian help, particularly in the areas of health, education and agriculture.
The new head of the British Army, General Sir David Richards, says it could take 40 years to get out of Afghanistan but Mr Key says New Zealand's direct military involvement should be over in five years.