The anti-wool advert hit the city of Glasgow back in February, following an investigation into the Scottish wool industry.
An eyewitness reportedly documented workers 'striking terrified sheep in the face with electric clippers, slamming their heads into the floor, beating and kicking them, and throwing them off shearing trailers'.
"Don't Let Them Pull the Wool Over Your Eyes: Wool Is Just as Cruel as Fur. Go Wool-Free This Winter," the advert, which was placed on the side of 20 buses, read.
The ASA has since ruled that the way sheep are raised do not match the conditions of those raised for fur, stating that shearing sheep for wool 'would not be regarded by consumers as being cruel'.
"The ad must not appear in its current form. We told PETA not to use the claim 'wool is just as cruel as fur' in [the] future," the ASA added.
'Confusing and disappointing'
According to the Telegraph, PETA hit back, arguing that shearing sheep is cruel as animals are 'not commodities' but 'sentient, intelligent, living beings with rich social lives'.
The charity branded the ruling as 'confusing and disappointing' but states it has amended the ad to say 'wool = cruelty to sheep'.