Farming leaders are lining up for a legal battle with the RSPCA over a "hypocritical" warning that a valued quality mark could be removed from food producers who support or allow the badger cull.
The NFU said its lawyers were combing through the details of a document sent by the animal welfare charity to producers around the pilot area in Somerset who belong to its Freedom Food scheme.
The wholly-owned subsidiary of the RSPCA is a benchmark of high welfare standards and in a letter to members says: "Based on the current science, welfare concerns and a realistic assessment of what is practical, a widespread cull of badgers is totally unacceptable to the RSPCA."
Freedom Food says that it believes it is "unacceptable to use lethal methods of wild animal control as routine practice".
The letter states: "As such Freedom Food would regard it as unacceptable for any of its members to voluntarily take part in a badger cull for the above reasons. To do so would also bring the scheme into disrepute and be a clear breach of the membership agreement, resulting in suspension."
NFU Director of Policy Martin Haworth said the organisation took "this threat to its members very seriously" and the letter was being examined by its legal team.
He added that questions should be asked of the RSPCA's objectives.
"It fully supports culling as a routine practice for deer, for example, with 350,000 removed annually. The same goes for rats and rabbits.
"Have Freedom Food members ever been suspended on these grounds?
"In this light, we can't help but see the Freedom Food letter on badger culling as hypocritical."
An RSPCA spokesman rejected the charge and said its stance on the badger cull was entirely consistent with their aims and policies.
He said Freedom Food farms agreed to abide by strict standards which included specifically prohibiting the inhumane killing of wild animals.
"It is therefore only permitted to cull wild animals that pose a threat to the welfare of farm animals, when other non-lethal methods have already been applied," said the spokesman.
"The culling method used must also be humane. These provisions are entirely in line with the RSPCA's position of opposition to the proposed badger cull."
The spokesman said that the RSPCA believed that the proposed shooting would make the situation worse in some areas through perturbation, the habit of displaced and possibly infected badgers of roaming.
"Consequently the RSPCA does not consider culling to be in any way justified on the grounds of protecting farm animals from harm and that badgers will suffer as a result of the cull.
"Consequently any Freedom Food farm participating in the cull would be in breach of RSPCA welfare standards and their agreement with Freedom Food."
The spokesman added that as the Government had not published specific boundaries, the organisation had written to all members in the general area to remind them of the provisions of their agreement and consequence of breaking it.
Meanwhile a group of professors from leading universities and zoological institutions have entered the debate.
More than 30 animal disease experts have written a letter to the Government arguing that culling badgers "is very unlikely to contribute to TB eradication" and they "urge the Government to reconsider its strategy".