(Reuters) – The U.S. Food and Drug Administration (FDA) said on Friday it has sent letters to Walmart Inc, Kroger Co and 10 other convenience store chains for selling tobacco products to minors.

In the letters, dated April 5, the FDA asked the companies to submit a plan of action within 30 days, describing how they will address and mitigate illegal sales to minors.

The 10 other retail chains include Casey’s General Store, Family Dollar Stores, 7-Eleven Inc and retail stores run by Chevron Corp, Royal Dutch Shell Plc, Exxon Mobil Corp, Citgo, Marathon Petroleum, Sunoco LP, and BP Plc. (bit.ly/2Rf82Ve)

“We all share the important responsibility of keeping harmful and addictive tobacco products out of the hands of kids. Retailers in particular are on the frontlines of these efforts to reduce the health consequences of tobacco use and nicotine dependence,” the FDA said in the letter.

The FDA has rolled out a Youth Tobacco Prevention Plan as part of its push to discourage teens from smoking.

“The new retailer letters are part of #FDA’s continued actions as part of its Youth Tobacco Prevention Plan and the agency’s ongoing commitment to combat youth access to all tobacco products, including e-cigarettes,” FDA spokesperson Jennifer Rodriguez said on Twitter here

In February, the regulator said it was taking action against certain retailers including Walgreen Boots Alliance for repeatedly flouting tobacco sale rules, including sale of cigars and menthol cigarettes to minors.

None of the 12 companies were available for comment after market hours on Friday.