Leaflets are being handed out during the busiest times of the day to encourage customers to eat elsewhere over claims that the fast food chain is not committed to poultry welfare.
However, KFC has hit back and denied the accusations, which are part of an ongoing Peta campaign.
A spokesman for KFC said: "KFC is committed to poultry welfare. KFC selects suppliers which meet or exceed UK and EU regulations on quality and welfare and regularly audits their performance.
"KFC represents less than 3% of the UK chicken supply, and uses the same suppliers as leading supermarkets. KFC does not operate or own its own chicken facilities."
Peta's global campaign was launched in 2003 after undercover investigations that claimed that the chain was allegedly not doing anything to eliminate abuse at factory farms and slaughterhouses that supply chickens to its restaurants.
The protest group claims that suppliers for KFC, which also produces poultry for retailers including Tesco, Waitrose, Marks & Spencer and McDonald's in the UK, "scald millions of fully conscious chickens to death every year and breed and drug them to grow so quickly that their legs break and their organs fail".
Peta is recommending that KFC adopts an Animal Care Standards programme and replaces electrical stunning and throat-slitting with controlled-atmosphere killing. It also wants switches to less cruel mechanised chicken gathering, birds bred for health rather than forcing rapid growth with drugs, and all welfare standards made verifiable.
KFC has said that all methods of slaughter, such as controlled atmosphere and electrical stunning used in the UK industry are approved by UK and EU legislation and KFC suppliers only use antibiotics as recommended by vets in response to disease.
In May, an ad for KFC became the most complained about ad in the UK to date after 1,671 people said they were disgusted by images of people singing with their mouths full, saying that it would encourage bad table manners.
The Advertising Standards Authority cleared the ad, created by Bartle Bogle Hegarty, saying it was made in good humour and did not breach the advertising code.
KFC's global sales have more than doubled over the past five years. It now has 693 outlets and a survey of 11,000 consumers last year voted it KFC best-loved fast-food brand.
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