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Citing government mandates and a rise in coronavirus cases around the United States, Walmart and Sam’s Club executives said Tuesday that they will require customers to wear face coverings starting July 20.

About 65 percent of the two chains’ 5,000 stores are located in areas where there is some form of government mandate on face coverings, and they want to make the policy consistent across all stores. Walmart has 21 locations in Maine and Sam’s Club has three.

The move comes one week after Gov. Janet Mills released an executive order requiring large businesses and food establishments to enforce rules that require face coverings as of July 8. The enforcement is part of the certification checklist that each business must agree to before reopening.

For some customers, face coverings have become more of a statement of personal choice rather than a health compliance. Some businesses and restaurants have not been enforcing face covering rules with customers who chafe against wearing them. People with certain health conditions are exempt from wearing masks, and business owners cannot ask them for a doctor’s statement, which inserts a difficulty into enforcing face coverings.

“We know it may not be possible for everyone to wear a face covering. Our associates will be trained on those exceptions to help reduce friction for the shopper and make the process as easy as possible for everyone,” wrote Dacona Smith of Walmart and Lance de la Rosa of Sam’s Club, both chief operating officers, in a message to store associates and customers on their website.

They said Walmart is considering solutions for customers who show up without a face covering. Walmart said it would post clear signage in front of its stores and has created the role of a health ambassador who will wear a black polo shirt and be stationed near the entrance to remind those without a mask of the new requirements. It also will have a single entrance to stores to better monitor adherence.

Sam’s Club associates will follow the same procedure at entrances and will provide free masks to customers who don’t have them.