The Food and Drug Administration issued letters to 12 companies earlier this month claiming their stores have sold tobacco products to minors and asking them to find ways to mitigate the sale of tobacco to underage consumers.

The letters, dated April 5, were sent to Walmart, Sunoco, Shell, Marathon Petroleum Corp., The Kroger Co., Family Dollar Stores Inc., Exxon Mobil Corp., CITGO Petroleum Corp., Chevron Corp., 7-Eleven Inc., BP PLC and Casey’s General Stores Inc. Each letter was signed by former FDA commissioner Scott Gottlieb.