The letter cited a statement put out by the U.S. Food and Drug Administration on Feb. 7 that said the Deerfield-based company has the worst track record among all pharmacies when it comes to selling tobacco products to children. About 22 percent of the more than 6,300 Walgreens stores inspected since 2010 have illegally sold the products to young people — a rate of violations higher than Walmart, Dollar General Stores and Rite Aid Corp. stores, according to the FDA.