The Food and Drug Administration (FDA) reprimanded Walmart, Kroeger, 7-Eleven and other chain stores for selling tobacco products to minors, CNBC reports.

The FDA gave the chains 30 days to submit a detailed plan explaining how they will reduce illegal tobacco sales to minors. If they continue these sales, the chains will face penalties and fines, the agency said.

“Retailers in particular are on the front lines of these efforts to reduce the health consequences of tobacco use and nicotine dependence,” the FDA said. “Because tobacco use is almost always initiated and established during adolescence, early intervention—including making sure tobacco products aren’t being sold to minors—is critical.”