PETA is urging Prince William and Kate Middleton to cancel an upcoming visit to the Calgary Stampede. Pawel Dwulit/Canadian Press

Prince William and Kate Middleton are being urged by an animal advocacy group to cancel a planned visit to the Calgary Stampede.

People for the Ethical Treatment of Animals has been a long-standing critic of the Stampede's rodeo events. The group says animals are injured and killed for the sake of entertainment.

In a written release, PETA says devices that are illegal in Britain — including electric shock prods — are used in the event "to cause great pain to the animals, who suffer broken bones, massive bruising, and internal bleeding, all for the sake of entertainment."

"The Calgary Stampede has long been synonymous with animal abuse," PETA President Ingrid Newkirk said in the release.

"The eye of the world rests on the Duke and Duchess, and they are walking into a hotbed of controversy over cruelty if they visit this vile rodeo."

The royal couple are to witness some Stampede events and preside over the kickoff of the parade on July 8 before leaving Canada for the United States.

In an open letter, Newkirk warns that William and Kate will be walking into a hotbed of controversy if they attend.

"The whole world eagerly watches your public endeavors," the letter reads. "It will be extremely upsetting if you attend the Calgary Stampede because your presence will be taken as an endorsement of the egregious animal abuse that residents have long protested. Please do not attend this event."