Packs of posh M&S Teriyaki Crackers have been removed from the shelves because they may contain prawn.
The snacks could pose a risk to anyone who is allergic to fish because the label has failed to list the ingredient.
The alert was issued for the allergen crustaceans which is also forbidden under the Jewish religion.
The high street giant said: "Customer safety is of paramount importance to Marks & Spencer and we take all issues regarding the production of our foods extremely seriously.
"Marks & Spencer has issued an Allergy Alert for its 60g bags of Teriyaki Crackers given the presence of prawn in a small number of packs, which is not mentioned on the label.
"Any customers in possession of this product who have a prawn allergy, or who wish to exchange the product, can return it to their nearest store where a full refund will be given.
"No other M&S products are affected. We apologise to our customers for any inconvenience caused."
The affected packs are all codes up to and including 8 November 2016 and a Unique Product Code: 00796859.
The Food Standards Agency added: "Some packs may contain prawns, which are not mentioned on the label, making it a possible health risk for anyone with an allergy to prawns.
"If you have bought the above product and have an allergy to prawn, do not eat it. Instead return it to the nearest Marks and Spencer store for a full refund."