Sainsbury’s has been accused of failing pet owners by not warning them that they were feeding toxic food to their cats.
Customers who opted out of marketing emails were also excluded from alerts about the nationwide product recall.
Applaws and Ava, two hypoallergenic cat food brands, are being investigated by the Food Standards Agency (FDA) after a spike in cases of pancytopenia.
Thousands of cats are thought to have died from the disease in the last twelve months.
The probe is exploring whether the products, manufactured by Fold Hill Foods, contain toxic compounds known as mycotoxins.
Although Sainsbury’s and other retailers recalled the brands on 16 June, several buyers were not alerted until a month later.
In an email exchange seen by the Guardian, Sainsbury’s told cat owner Linda, 57, that she had not been sent a recall notice because she had asked not to receive promotional emails.
“You have not received an email notification regarding our cat food recall as you have unsubscribed from our marketing emails, which is also where our recalls are provided from,” the supermarket said.
Linda’s cat was unharmed after she saw warnings about the cat food through Facebook and from the consumer group Which?
“I saw nothing from Sainsbury’s, social media or otherwise, until an email arrived from them weeks later,” she said.
“I really think Sainsbury’s has let customers down, and their product recall policy needs to be reviewed.”
A Sainsbury’s spokesperson admitted that a flaw in its product recall protocol meant some pet owners had not been alerted for several weeks.
“A systems issue led to a delay in some customers receiving our recent recall notice,” they said.
“We put this right as soon as it was identified and we continued to display the recall notice in store and online.”
Members of a Facebook group for cat-owning Sainsbury’s customers have previously complained that the signs had not been prominently displayed.
Over 100 cat owners are believed to have contacted law firm Leigh Day, which is exploring the possibility of legal action after the FDA concludes its investigation.