New Zealand is working with Australia to consider a response if Japan resumes whaling in the Southern Ocean - with legal action remaining a possibility.
Deputy Prime Minister Bill English told Paul Henry that New Zealand and Australia were working together to look at what kind of response could be made.
Mr English was asked if New Zealand could send a frigate to monitor Japanese whaling boats, but said he would not want to prejudge that.
"There may be legal means, which were the steps taken last time."
He said Prime Minister John Key would raise the issue with Japanese counterpart Shinzo Abe this week "to maintain the diplomatic pressure".
Mr Key is in Paris for the COP21 climate talks, and has already labelled the whaling decision "appalling" and a show of bad faith.
Japan has advised the International Whaling Commission it will resume whaling in the Southern Ocean but has reduced its intended take.
That is despite an International Court of Justice ruling last year that Japan's previous whaling programme was unlawful because it was not for genuine scientific research.
Australia has also condemned the decision and took the case to the international court, a move that New Zealand supported.
The Green Party has called for the Government to send surveillance aircraft or vessels to monitor the whaling. Mr Key said that was an option but it was problematic because the area was in international waters.