The Government is not doing enough to help imprisoned anti-whaling activist Peter Bethune, his father Don Bethune says.

The Hamilton man has challenged the Government to take a firmer stance, like that of Australia, against whaling.

Peter Bethune, was skipper of the ill-fated Sea Shepherd vessel Ady Gil, which was involved in a Southern Ocean collision with the Japanese whaling ship Shonan Maru II in January, and later sank.

A few weeks later, he boarded the Japanese vessel in an attempt to arrest the ship's captain.

He was captured by the crew and taken back to Japan where he is in prison awaiting trial on several charges.

Don Bethune told the Waikato Times the situation was becoming increasingly frustrating, and he was now going public with his concerns.

He echoed sentiments of Labour's foreign affairs spokesman, Chris Carter, who has claimed the Government is putting off acting on the issue because of trade and export concerns.

Last week, Australian Environment Minister Peter Garrett voiced concern over the New Zealand Government's apparent support for a pact to legalise limited whaling.

Don Bethune said the Government appeared unwilling to become involved in the situation, and its attitude implied "we can't interfere with the Japanese judicial system".

A spokesman for Foreign Affairs Minister Murray McCully's office said consular staff in Tokyo had visited Peter Bethune four times, and were providing all the assistance they could.

The Government could not wade into the legal situation and demand Pete Bethune's release, and "had to respect the judicial system of sovereign nations", he said.

Mr McCully's office also rejected Don Bethune's claim the Government had back-pedalled on the whaling issue, and said it remained opposed to continued whaling by the Japanese fleet.

Last week, Mr Carter said Peter Bethune was being made a scapegoat by Japanese authorities, and the New Zealand Government should do more to ensure he was not victimised.

Peter Bethune has been charged with trespassing on the Shonan Maru II, injuring a crewman, obstructing commercial activities, vandalism and carrying a weapon.

If convicted, he could face up to 15 years in jail.