The Food Standards Agency said that Waitrose had removed from sale its 85g Waitrose 1 bars in White Chocolate, White Chocolate with Matcha Tea & Pistachio, Milk Chocolate with Pistachio, Almond & Hazelnut and Milk Chocolate with Feuilletine & Sea Salt.
No other Waitrose products are known to be affected.
The company said in a statement: "We are recalling the above products, as there is the potential that a small number of bars may be contaminated with pieces of plastic. Customers who have purchased any of the above products should not consume them, but return them to Waitrose for a full refund.
"We apologise for any inconvenience to our customers."