Prime Minister John Key says he would be "deeply disappointed" if Japan were to resume whaling in the Antarctic Ocean next year.
Japan is seeking international support for a revised programme it hopes will meet the conditions of hunting minke whales for scientific research purposes.
The new programme would aim to comply with an International Court of Justice ruling in March, which found that the number of whales that Japan killed did not justify its research claims.
The court action was taken by the Australian Government, and supported by New Zealand. Attorney-General Chris Finlayson gave evidence on behalf of New Zealand during the court case last year. The decision was 12 to 4 in Australia's favour.
Japan's Fisheries Agency wants to submit a revised programme to the International Whaling Commission's scientific committee later this year, which it hopes will address the problems cited by the court.
Today Mr Key sent a strong message that New Zealand opposed the resumption of Japanese whaling in the Southern Ocean.
"I'd be deeply disappointed. New Zealand was part of the legal case that was taken to the ICJ in relation to Japanese whaling activities.
"The message from the ICJ was very clear, and the message to Japan should, in my opinion, be extremely clear. We don't want them undertaking what they propose and claim to be scientific whaling, but really in our view is not.
"We think they should stay out of those waters."
He said sending New Zealand navy ships to the ocean would probably be a step too far.
"Almost certainly not. That hasn't been a position the Government's adopted."
He said he would have to talk with Mr Finlayson before deciding whether New Zealand would oppose a plan from Japan in the International Whaling Commission.
Whaling for research purposes is exempt from the 1986 international ban on commercial whaling.
After the ICJ ruling, Foreign Minister Murray McCully cautioned that Japan might try to alter its programme to comply with the ruling.
"Our task is to make sure that we carry out a diplomatic conversation that dissuades them from embarking on that course," Mr McCully said in April.