Consumer group Which? has said Tesco could be breaking the law over how it displays Clubcard prices.
The group has reported the supermarket to the regulator, the Competition and Markets Authority (CMA) and says Tesco does not explain the unit price of deals clearly enough to shoppers, making it hard for them to determine the cheapest product.
Which? head of food policy Sue Davies told the BBC: "They have a duty to ensure pricing is clear so that customers can get the best value. Tesco's unclear Clubcard pricing is at best confusing for shoppers struggling with soaring food inflation and at worst, could be breaking the law.
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"This is simply not good enough from the UK's biggest supermarket. Tesco should think of its customers and act now to introduce clear unit pricing on all offers, including Clubcard promotions, so shoppers can easily find the best value items."
But a spokesperson for Tesco said the company had sought advice and approval from its local trading standards office in Hertfordshire where its headquarters are based.
"Providing great value and clear pricing is really important to us, we are supportive of calls for greater clarity on the regulations in this area," the spokesperson told the BBC.
"However, given that we are complying with all the current rules, we are disappointed that Which? has chosen to make these ill-founded claims against our Clubcard Prices scheme, which helps millions of households get great value week in, week out."
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