Animal rights extremists threatened to make life a "living hell" for employees of a nursery linked to an animal testing laboratory, it has emerged.
Firms linked to Huntingdon Life Sciences have been targeted
A letter was sent by the Animal Rights Militia to Leapfrog Day Nurseries because of a child care scheme for Huntingdon Life Sciences.
The note, seen by Channel 4 News, said employees of the nursery would "pay the consequences" for the links.
The scheme was withdrawn by the nursery to protect children and staff.
Leapfrog Day Nurseries - Britain's largest childcare provider - has 102 nurseries nationwide, with units in Beds, Bucks, Herts, Cambs, Essex and Northants.
They administered a scheme for Huntingdon Life Sciences to give employees child care vouchers which can be used at any nursery.
Huntingdon Life Sciences have long been targeted by anti-vivisection extremists. Supports, including the government, argue that its work is needed to prompt medical breakthroughs.
The letter read: "The company you work for is working with Huntingdon Life Sciences. This is a disgusting and cowardly act. You have a choice.
"You can walk away from those sick monsters or you can personally face the consequences of your decision."
The note went on: "Not only you but your family is a target.
"... Sever your links with HLS within two weeks or get ready for your life and the lives of those you love to become a living hell."
A spokesman said they were not aware that any children from Huntingdon Life Sciences attended their own nurseries.
In a recent spate of animal rights activism, campaigners recently claimed responsibility for leaving a device outside the home of Paul Blackburn - the corporate controller of GlaxoSmithKline - earlier this month.
Huntingdon Life Sciences carries out cancer and other medical research on animals, which the government has described as vital, but have come under fire from campaign groups.