Extremists opposed to the badger cull have been posing as officials from Natural England and the NFU to dupe farmers into revealing details of pilot culls on their land.
A source involved with the cull project told the Western Morning News that as a result of the tactics all farmers were now being advised to carefully check the details of anyone calling at their farms claiming to be an official.
He said of the protesters: "They are trying to get farmers' details and then they go away and research those details before ringing up the farmers and making threats.
"We are saying to all farmers that if they are approached by people and they cannot be absolutely sure of their identity they should say nothing and send them away. They should take any details of vehicles and report them to the police."
Pilot culls were approved by the Government earlier this year in West Gloucestershire and West Somerset to find out if shooting badgers could be carried out efficiently as a means of reducing badger numbers and bringing down the incidence of bovine TB on farms.
Opponents claim a cull could make the situation worse.
Despite the heightened tension since the first cull licence was granted for an area of West Gloucestershire last month, attitudes among the cull teams remain positive, the WMN was told.
But the spokesman for the cull operators, who asked not to be named, indicated talks with the police in Gloucestershire were still going on to ensure officers' concerns about the safety of protesters could be met to allow the cull to proceed. Strict rules are in place to avoid accidents, he said.
Cull teams had been told that if they came across protesters in the area where a cull was planned they should "drive straight on by". And he said if any protesters were met at night when the cull teams were out, the contractors were instructed to make their rifles safe by removing the bolts and withdrawing.
But he also warned that the culls would be taking place on private land, well away from rights of way, and anyone found trespassing could be guilty of interfering with lawful action.
"We hope the police will act firmly to support what is a lawful operation," he said. "All those involved have had all the necessary health and safety training. There is absolutely no danger to members of the public from shooting at night."
He admitted the ferocity of opposition to the cull and the intimidation aimed at those who might be involved had been "upsetting." But he said the resolve of those who wanted to get the job done remained as strong as ever.
"As a general rule the resolve of the farmers is good," he said. "They and the contractors want to get the job done because they believe it is necessary and has been lawfully agreed and properly organised."