The navy will be using only two of the navy's four inshore patrol vessels because it does not have enough sailors to crew them.
Labour says the situation is the result of the government putting the country's security at risk with "unrealistic" cost cutting.
"Morale is at an all-time low and with Defence Force personnel lining up to leave, the navy has found itself unable to adequately crew its inshore patrol vessels," Labour's defence spokesman Iain Lees-Galloway said.
"That leaves our economic zone vulnerable and makes a mockery of the government's supposed concern about protecting our border from boatloads of asylum seekers."
The inshore patrol vessels, Rotoiti, Hawea, Pukaki and Taupo, each need 36 personnel and the four need to spend about 950 days at sea each year.
The Defence Force last year reported a record high attrition rate of 19 per cent, following a process of civilianisation, where 304 uniformed roles were changed to civilian ones.
It was a part of a drive to save $355 million by 2015.
But Chief of Navy, Rear Admiral Tony Parr, says the navy will still be able to perform its inshore patrol duties while it recruits more personnel.
It will get other ships to take up the inshore patrol work when needed.
It would also change its policy of having all ships available for duty if they are not in for maintenance, to reduce the stress on crew and allow them to further train.
"We've recognised that it is not only the ships that must rotate through maintenance, but also our people."
He said two, but often three, of the inshore patrol vessels would be available to patrol at any given time.
Rear Adml Parr says the Defence Force's senior leadership have committed to lifting morale and slowing the number of people leaving.Dr Coleman was not immediately available to respond to Labour's accusations.
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