Police are investigating an anonymous threat that milk supplied to a dairy plant had been poisoned.
A man claiming to be a farmer who had been put out of business because of recent financial problems at the Westbury Dairy in Wiltshire told officers he had tampered with the milk.
All supplies at the plant have now been isolated while urgent tests are carried out - police say there is no risk to the public.
The threat came days after the troubled dairy, which supplies butter and milk powder across England and Europe, called in the receivers.
'Hugely irresponsible'
Last week the former United Milk plant, which employs some 100 workers, was bought by Westbury Dairies - a consortium of three milk co-operatives.
But about 300 farmers are still said to be owed £30,000 each for milk they had supplied to the £45m plant.
Others could lose their share of the £12m they invested when the dairy was established in 2001.
A Wiltshire Police spokesman said: "The caller, who is believed to be a farmer, stated that he has poisoned his milk delivery and will continue to do so.
"He has stated this is because he has been made bankrupt."
The National Farmers' Union has condemned the action as "hugely irresponsible."