The Japan Coast Guard plans to arrest a New Zealand anti-whaling activist for trespassing on a ship in Japan's whaling fleet.

Pete Bethune boarded the Shonan Maru No. 2 in the Antarctic Ocean last month. He blames the skipper of the ship for the loss of his high-tech trimaran, the Ady Gil, in January.

The Shonan Maru No. 2 arrives in Tokyo on Friday. If prosecuted for trespassing on a ship, Bethune faces up to three years in jail.

Meanwhile Labour is accusing Prime Minister John Key of kowtowing to pressure from whaling nations. It comes after New Zealand's representative at the International Whaling Commission Sir Geoffrey Palmer endorsed a proposal allowing Japan, Norway and Iceland to resume commercial whaling, but reduce their total catch during the next ten years.

It is part of the Government's aim of reaching a diplomatic agreement.

Labour's Foreign Affairs spokesman Chris Carter claims Mr Key has turned New Zealand from being a world leader in marine mammal conservation to being an active advocate for the resumption of commercial whaling.