Several trusts that fund Oxford University are being targeted by animal rights campaigners who are trying to scupper plans to develop an animal research centre in the city.
The animal rights group Speak is putting pressure on the university by writing to funders in the hope that they will sympathise with its cause and cease funding.
"Funding from trusts and private companies amounts to £92m a year," said Speak spokesman Rob Cogswell. "Without that money, the university would become financially insolvent and would have to drop its construction project."
Speak provides contact details of various funders on its website and encourages its supporters to write to them. Last year, the group's campaign against the development of an animal research centre at Cambridge University led to the cancellation of the project.
One trust, the Tubney Charitable Trust, funds conservation projects and initiatives to aid the welfare of farmed animals. It recently received letters from a number of individuals asking it to withdraw its funding, even if it does not contribute to animal experiments. But Sarah Ridley, the trust's director, said it would not.
The Sutton Trust has also received letters from campaigners, but said it had not complained to the police because the letters were not threatening.
Another research and education charity, the Leverhulme Trust, received emails a few months ago and said it did not know who was behind the campaign.
But it did notice that leaflets distributed during a protest outside its London office a few months ago were from Europeans for Medical Progress, a UK not-for-profit medical research organisation with a charitable arm.
The charity, which aims to expose the human health hazards of animal experimentation, said it knew nothing about the protests against the Leverhulme Trust.
"We are not an animal rights organisation," said Kathy Archibald, director of Europeans for Medical Progress and a former researcher at Animal Aid.
"It's outside our sphere. Our goal is to find out whether animal research helps or harms human health. We have no connections with any animal rights campaigners and we are not taking any stand on Oxford. Our opponents, such as the Research Defence Society, are very keen to label us as animal rights protesters in order to diffuse our message."
She added: "Animal rights campaigners will use our brochures; there is no way to stop that. But I do regret that it gives the impression we support them."