Tesco shoppers have complained that matzah meal in its Pesach section is not certified for the festival.
Lesley Morris bought two packets from the Borehamwood store, discovering only after returning home that one was not kosher for Passover.
Another woman encountered the same problem with an online order from the Borehamwood branch and a customer at Tesco in Brent Cross also reported finding non-Pesach certified matzah meal among its Passover display.
Mrs Roberts - who did most of her Pesach shopping at Tesco - said she was changing her crockery over for the festival when she "happened to glance at the packet" and was shocked to discover that it was not kosher for Passover.
A Tesco spokesman said staff did their "very best to make sure that products always match shelf-edge labels. We have asked staff to check our kosher goods regularly to ensure this is the case."
There was also a complaint from an Asda customer whose online order was delivered with the blue Rakusen's matzah, which cannot be eaten during the festival.