A vegan student was served a pork sausage rolls in Greggs in a Kent branch of the store.
Sharleen Ndungu says she 'burst into tears' and had 'heart palpitations' after biting into one of the two rolls, and realizing it contained animal meat.
Ndungu, who made a video about the situation which she has since deleted, said she went straight back to the store to demand an apology. She was offered a £2 refund.
She then phoned Greggs' head office and was offered a £30 voucher, but turned that down, saying she wants a public apology, which would raise awareness of how important it is to label foods properly.
"If I was allergic to pork or any of the ingredients that were inside that dirty sausage, I literally could have died," she said.
"Some people, namely meat-eaters, might think I'm over exaggerating but I could have died."
According to a statement from Greggs, the chain is investigating the incident.
"We have apologized to the customer for this incident," said a spokesperson. "We are investigating to ensure this situation can be avoided in the future."
Greggs' sausage rolls have different pastry patternation to distinguish them.
The pork sausage rolls (see top photo) have slashes cut into them, while the vegan ones have a more elaborate criss-cross pattern.