An organisation representing medical charities has been condemned for compelling its members to make a public declaration of their support for animal testing.

The Association of Medical Research Charities (AMRC) has made it a mandatory condition for all its 133 members that from November 20 they post the message on their websites.

Any charity wishing to join the association after that time will have to abide by the same rule.

Anti-vivisectionists accused the AMRC of being "outrageously authoritarian" and stifling dissent over the controversial issue of animal research.

The group Animal Aid is writing to all AMRC members urging them to challenge the move and stand up for their right to an independent point of view.

While the vast majority of AMRC charities provide funding for animal experiments, a sizeable minority do not.

Animal Aid stressed that expulsion from the AMRC would come at a heavy price because of the association's powerful reputation and political connections which help attract donations to its members.

Director Andrew Tyler said: "It is a mark of deep insecurity that AMRC is throwing its weight around by insisting on the swearing of a pro-vivisection public oath.

"While the pro-vivisection lobby is currently making great play of its professed commitment to 'openness', AMRC's new dictatorial edict is designed to silence members who have doubts about animal research and close down the debate.

"This is an outrage considering that it is not just animal suffering that is at issue, but the growing doubts over the value of animal-based research to human medicine."

Michelle Thew, chief executive of the British Union for the Abolition of Vivisection (BUAV), said: " We believe the requirement by AMRC for its members to publicly declare support for animal experiments demonstrates just how concerned the animal research industry is about the widespread public awareness and concern there is surrounding the use of animals in laboratories.

"We call on AMRC to also require its members to publish project licences on their websites so that details of the experiments carried out on animals by charities are available to the public, including the numbers, species and levels of suffering involved."

The AMRC has always stated that it backs the use of animal experiments when no other alternatives are available.

While individual members were already expected to agree with this position, from the date of the association's next annual general meeting on November 20 they will be required to declare their support publicly to would-be donors.

Guidance has been given to the charities on the wording to post on their websites. Those not funding animal research are advised to state: "Our research strategy is to focus on (insert) and so we do not currently fund research using animals. However, as a member of AMRC we support the principle of using animals in research when it is necessary to advance understanding of health and disease .. "

Animal Aid believes its "Victims of Charity" campaign which it claims has highlighted "cruel and medically invalid" charity-funded animal experiments has put the AMRC under pressure to present a united front.

A spokesperson for Epilepsy Action, an AMRC charity that does not provide funding for animal experiments, said: " Epilepsy Action only funds non-laboratory research. We will look at our research policy when we are contacted by AMRC."

Two other charities believed to be in the same category refused to comment.

The AMRC's 133 members spend more than £1.3 billion a year on medical research. They include giant funding institutions such as the Wellcome Trust and Cancer Research UK.

Aisling Burnand, chief executive of the AMRC, said: "Whether they are funding research using animals, or their funding is focused in other areas of medical research, all 133 AMRC member charities stand together in support of the principle of using animals in research when it is necessary to advance understanding of health and disease and to develop new treatments for patients. This research only takes place where there is no alternative available.

"The Concordat on Openness on Animal Research is a major statement of intent by the whole of the medical research community that openness and transparency over the use of animals for scientific research is non-negotiable. 85 organisations, including universities, charities, commercial companies, research councils, umbrella bodies and learned societies have signed.

"AMRC was closely involved in the development of the Concordat and, in signing, we signal the medical research charity sector's united commitment to communicating openly about research involving animals.

"At the 2013 annual general meeting, our members unanimously agreed to link to the AMRC position statement on the use of animals in research from their websites. We are working with our members to share best practice and ensure researchers exceed the regulatory requirements to improve animal welfare and science."

Although the decision to bring in the new rule was passed at the last AGM, the public declaration only becomes compulsory from November 20.