Tesco, Asda and Waitrose will not let shoppers into their stores if they are not wearing a face covering, the British supermarket groups said on Tuesday, joining rivals Sainsbury's and Morrisons which made the policy change a day earlier.
With COVID-19 infection numbers rising sharply, the UK government has expressed concern about the spread of the virus in supermarkets, with some people breaching rules by not wearing masks while shopping.
Non-essential retail, restaurants and bars are shut across Britain, leading to a high level of demand for supermarkets and other food stores.
"To protect our customers and colleagues, we won’t let anyone into our stores who is not wearing a face covering, unless they are exempt in line with government guidance," market leader Tesco said in a statement.
"Our colleagues are working hard in difficult circumstances to make sure everyone can get what they need, and we’d ask everyone to please be kind, patient and respectful as we all work to keep each other safe."
Tesco said it was also asking customers to shop alone unless they are a carer or with children.
It has also put in additional security in stores to manage the change in stance.
Asda issued a similar statement. It said if customers had forgotten a face covering, it would continue to offer them one free of charge.
"But should a customer refuse to wear a covering without a valid medical reason and be in any way challenging to our colleagues about doing so - our security colleagues will refuse their entry," it said.
The John Lewis Partnership also said face coverings would be mandatory at its Waitrose supermarkets.
The British Retail Consortium, which represents more than 170 major retailers including the big supermarket groups, said on Monday it was the police's responsibility to enforce face coverings and called for their support.