The RSPCA and other animal rights groups have criticised a music festival for dyeing its sheep bright pink.
The animals have become a signature sight at Latitude Festival in Suffolk over the past 14 years.
But the practice has been labelled "ignorant and cruel" by Peta activists, while a petition calling for change has nearly 3,000 signatures.
Organisers said the water-based dye is not harmful and that "sheep welfare is the farmers' priority".
A spokesman for the RSPCA said it would be writing to Latitude organisers about the sheep.
"We want all animals treated with kindness and respect and would discourage people from painting or dying animals for novelty purposes," she added.
Criticism began when a video was posted on the festival's Instagram page showed the release of the animals at Henham Park site.
While a number defended the tradition, saying they were "happy" a natural dye was used, other posts describe the colourful sheep as "disgusting", "pointless and horrible".
One commentator wrote: "What a ridiculous instance of animal exploitation for entertainment, profit and some Instagram likes."
A petition to end the practice has been backed by 2,800 people in three days, calling the sheep "sentient beings, not party props".
A statement on the festival website said: "The sheep welfare is the farmers' priority and we are more than happy with both the dying and grassing available at the festival.
"The sheep are dip-dyed using natural, water-based dye. They are used to dip-dyeing as part of their normal farm life."
Farmers carry out daily checks to ensure the welfare of the sheep, it added.
The sell-out festival ran from Thursday to Sunday, with an estimated 40,000 people attending to see live music, arts and comedy.
Headliners Stereophonics stepped in to replace Snow Patrol on Saturday night's main stage, while other big-name performers included George Ezra and Lana Del Rey.
- 26 June 2019
- 5 January 2017
- 16 July 2015