'Why I stick pro-vegan stickers on meat in supermarkets'
A customer says she was shocked and felt "emotionally blackmailed" after finding an anti-meat sticker on a packet of spaghetti bolognaise.
Leah Mallett bought the ready meal at a Morrisons supermarket in Leeds.
Marc Gurney, who runs a vegan campaign in Brighton, says he wants people to think about what they're eating.
"I think it's important that people understand that it's not right for an animal to be killed when there are so many alternatives to animal products."
He's told Newsbeat that it's also important people think about what animals go through in the food industry.
"If this girl was horrified and scared then perhaps she needs to think twice about what she puts on her plate," he says.
"She needs to consider what the cow was going through while it was experiencing a brutal torture."
It's understood that the case in Leeds isn't a one-off and is part of a wider campaign.
The note that got people talking shows a cow which looked distressed along with the words: "My name was Chloe. I wanted to live. Your 'personal choice' killed me. DON'T BUY IT."
The news has been shared by Vegan Twitter accounts.
One customer who picked up a meal with the message on the inner sleeve told several news websites that it made her feel "horrible".
We put it to activist Marc Gurney that what he was doing was breaking the law.
"The stickers are usually placed on the side of the package," he told us. "You stick at your own risk.
"The point is we are being bombarded with images of dead animal flesh and what we are doing is raising consciousness.
"I'm not sure about the legal side but the worst that may happen is they throw you out of the supermarket."
We also put it to him that his stickers shocked and upset the woman in Leeds who saw a similar one on her microwave meal.
"They are peaceful and none graphic," the activist told Newsbeat.
"They are sending out a provocative message for people to make the connection.
"We have to be a voice for these animals for the obvious reason.
"Times are changing and there are a hell of a lot of vegan products that are a replacement for animal products."
The issue has divided opinions on social media and not everyone is sympathetic to the stickers and the people putting them on meat products.