Scientists are being targeted by animal rights activists, the University of Nottingham says.
Letters are being sent to their neighbours advising them to put pressure on the scientists to stop experiments on guinea pigs.
The letters suggest protests may be held near the homes if the work continues.
The University has condemned the letters, which have a Staffordshire postmark, and police are investigating.
The letters purport to come from an employee at an enterprise licensed to breed guinea pigs for research purposes.
Staffordshire Police say this man is not known of at the farm.
University spokesman Philip Dalling said: "The university deplores this tactic which is a crude, inaccurate attempt at intimidation.
"It's very unhelpful to treat people in this way that are making a huge contribution in the fight against disease.
Chance to defend work
"This campaign is not just restricted to Nottingham; it is happening all over the UK at research universities."
The letters contain a veiled threat that "unsavoury" characters could appear in the neighbourhoods where the scientists live.
Robin Webb, press officer, Animal Liberation Front (ALF) said: "If these scientists are proud of what they do, then this gives them the opportunity to stand up and defend it.
"If they are ashamed of what they do, then it gives their neighbours the opportunity to say 'we don't like what you are doing and we don't like you living next door to us'.
"Many of them practise useless experiments on animals and they only do it to try to advance their careers within the academic community."
Mr Webb denied the letters were from the Animal Liberation Front.
The letters have been handed over to the police.