As the International Whaling Commission nears the end of its annual meeting here, almost a third of its members are considering establishing a rival organisation.
They bitterly resent its agreement to make conservation a priority.
Japan has been the focus of protests at the conference
They say this change flouts international law and tries to subvert the commission's purpose.
One delegate says it is now so divided that it can no longer function.
The commission was set up in 1946 with a dual mandate: to regulate whaling, and to conserve whales.
In the last 20 or so years a majority of members have stressed whale conservation, and in effect have sought to postpone the resumption of commercial whaling indefinitely.
That remains suspended under a moratorium in force since 1986, though thousands of whales have been killed since then.
Japan kills 6-700 a year for what it says is research, and Norway kills a similar number in a commercial hunt allowed to continue because it objected to the moratorium.
Now Iceland wants to restart research whaling, which the IWC's rules permit.
The three countries say the IWC should conserve whales simply so there are enough to hunt: they claim the species they kill are abundant enough for the catch they take.
It's as if you thought you'd joined a football club, only to find it had become a stamp-collecting society
Japanese Fisheries Agency
Earlier in the week the commission adopted what is called the Berlin Initiative, which says, in effect, that conservation is a priority for the commission in its own right, irrespective of any need to hunt whales.
With their usual backers in the Caribbean and elsewhere, Japan, Norway and Iceland have released a statement protesting bitterly at the adoption of the initiative.
'polarised and dysfunctional'
It is signed by 16 of the 51 commission members: Japan says only procedural problems prevent Russia from signing too.
It says the decision "will essentially destroy the already polarised and dysfunctional IWC".
"It is an attempt to change the fundamental objectives of the international convention for the regulation of whaling by a simple majority vote.
"Such action is contrary to applicable international law... [and] is an attempt to subvert the purpose of the IWC."
The statement says the adoption of the initiative "raises concerns as to whether the IWC can function in the way foreseen".
With the lack of progress on completing the commission's revised management scheme, designed to achieve a scientifically sound way of allowing the moratorium to be lifted, the signatories say they have "an increased interest in examination of alternatives" to the IWC.
Threats to set up a rival body are not new, but Japan says this time it is in earnest.
Turning point year?
Joji Morishita, a senior official of its Fisheries Agency, is a member of Japan's delegation.
He told BBC News Online: "They've changed the rules. It's as if you thought you'd joined a football club, only to find it had become a stamp-collecting society."
"We could decide to withhold our IWC subscription, or set up a new regional or global body competent to do the commission's job. We'll review our options back in Tokyo.
"This year could be a turning point for the IWC. The Berlin Initiative is an ultimatum, and the commission's now so polarised it can no longer function as a viable organisation."
Minoru Morimoto, head of the Japanese delegation, said he was "particularly unhappy at the attitude of the US delegation" for its "excessively strong" opposition to Japan's request to be allowed to kill 150 whales annually for five years off its coasts.
Signatories to the statement are Antigua and Barbuda, Benin, Dominica, Gabon, Grenada, Guinea, Iceland, Japan, Mongolia, Norway, Palau, Panama, St Kitts and Nevis, St Lucia, Senegal, and the Solomon Islands.