Breeders of Gloucester old spot pigs have accused Waitrose of mis-labelling one of its bacon products.
Experts said pork described by the supermarket as coming from the rare native breed on its labels, was little more than "mongrel" meat.
They claimed the bacon was the product of a Gloucester old spot boar mating with a commercial sow.
Waitrose said the parentage of the pigs was clearly labelled, but added that all meat-labelling was being reviewed.
The Gloucester Old Spot Breeders Club said a sticker on the back of the packet, referring to free-range Gloucestershire old spot-sired pigs, was misleading.
Breeders said the supermarket was taking advantage of a growing market for rare breeds meat.
A statement from Waitrose said: "Cross-breeding is strongly rooted in the heritage of British agriculture and provides a way to improve eating quality in a way that is affordable for our customers and commercially viable for the farmers and breeders with whom we work.
"We believe that the work of native breed producers should be celebrated and have never intended to compete with them.
"Our buying team very much want to continue discussions with The Gloucester Old Spot Society and have already arranged a meeting to do just that."
The pigs are a traditional breed from the apple orchards of Gloucestershire.
Local folklore said the spots on the pigs' backs were bruises from falling fruit.
The first pedigree records of the pigs began in 1913.
They were traditionally known as the orchard or cottage pig, as they lived in gardens and smallholdings and were reared largely as domestic animals.