Trading Standards chiefs in Leicester are demanding to know why Burger King's main branch in the city has been selling cans of Coca Cola and Fanta with Arabic and German labels.
The Granby Street branch was investigated after members of the public complained about the labelling. Staff at the branch said they were doing it because their drinks machine was broken.
Selling drinks that are not labelled in English carries a fine of up to £5,000, because of the risk of customers who suffer from allergies not knowing what they are drinking.
If, however, the cans had been opened by the retailer and poured into a container, no laws would have been broken.
Leicester's Trading Standards spokesman, John Fox, said he was surprised to find an international company, with the reputation of Burger King, selling the drinks.
"They are selling a pre-packaged product, which becomes illegal if there is no English labelling," he said.
Leicester Trading Standards are now investigating the matter and have asked the food giant for an explanation.
A spokeswoman for Burger King said it would be carrying out its own investigation and were "grateful for the matter being brought to their attention".
By Roger Bushy