McCartney, a strict vegetarian for the past 30 years, was outraged after discovering the McDonald's in his hometown had hung photographs of himself and his former band mates John Lennon, Ringo Starr and George Harrison inside the restaurant.
Geoff Baker, a spokesperson for McCartney, said: "What sort of morons do McDonald's think Beatles' fans are?
"It's ridiculous and insulting to use images to peddle hamburgers. Fans should boycott McDonald's, and not just in Liverpool."
A McDonald's spokesperson said the pictures were to "acknowledge the outstanding contribution the Beatles made to both local and global culture."
McCartney and his late wife Linda had their own range of vegetarian meals, while he is president of the Vegetarian Society of Great Britain and an ambassador for People for the Ethical Treatment of Animals.
A PETA spokesperson said: "He became a vegetarian after watching lambs play in a field outside his home and surely would not want anyone to use his likeness to help promote meat.
"We hope anyone who sees his picture on the wall will be reminded that he's a vegetarian and skip the Big Mac for a veggie-burger."