A North Carolina diner that received national attention for discounting praying customers' meals has ended that non-official policy.

Mary's Gourmet Diner received a letter this week from an atheist organization informing the restaurant that the practice was illegal.

The Winston-Salem diner was taking 15 per cent off patrons' bills if their server spotted them praying. Owner Mary Haglund said she had been offering the discount for four years.

The price reduction, which was not advertised and was not an official policy of the restaurant, drew attention after a customer, Jordan Smith, shared her Mary's Gourmet Diner receipt on Facebook. The photo caught the attention of an Orlando radio station, Z88.3 Orlando, who shared the photo with their nearly 60,000 followers.

The receipt showed a $40.50 subtotal, followed by a 15 percent discount for "Praying in Public."

The Freedom From Religion Foundation took issue with the practice, as outlined in a letter sent Monday.

"It is illegal for Mary's Gourmet Diner to discriminate, or show favoritism, on the basis of religion," staff attorney Elizabeth Cavell wrote.

"[The] promotional practice favors religious customers, and denies customers who do not pray and nonbelievers the right to 'full and equal' enjoyment of Mary's Gourmet Diner," she continued.

"Any promotions must be available to all customers regardless of religious preference or practice on a non-discriminatory basis."

Rather than fight the issue in court, Haglund decided to end the "Praying in Public" discount.

"We at Mary's value the support of all of our fellow Americans," a letter posted on the door of the restaurant read.

"While you may exercise your right of religious freedom at this restaurant by praying over your meal to any entity or non-entity, we must protect your freedom from religion in a public place.

"We are no longer issuing the 15% praying in public discount. It is illegal and we are being threatened by lawsuit. We apologize to our community for any offense this discount has incurred."

Haglund stated that she did not know the legality or illegality of the discount when she began offering it, and did not see the gesture as a religious statement.

"This is a thankful thing. It's just an attitude of gratitude," she told WGHP last week.