Walmart and Sam's Club will hike the minimum age for buying tobacco products to 21, and will no longer sell the fruit flavored vaping systems that have become popular with teenagers.

The new age requirement will kick in on July 1 Walmart said Wednesday, and will apply to the sale of e-cigarettes as well. But even adults will no longer be able to buy the electronic nicotine systems that taste like desserts or fruit, with Walmart saying it plans to phase out those products.

"We unequivocally acknowledge that even a single sale of a tobacco product to a minor is one too many, and we take seriously our responsibilities in this regard,'' John Scudder, Walmart's U.S. chief ethics and compliance officer, said in a letter addressed to the U.S. Food and Drug Administration.

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In March, the FDA accused 15 national retailers, including Walmart and several gas station chains, of selling tobacco products to buyers who were underage.

The agency said then that it was considering enforcement actions "to address high rates of violations" at the retailers after more than 1 million undercover checks this decade reportedly found high rates of sales to minors.

Walmart was among the chains to have tobacco sales violation rates of between 15 percent and 24 percent, according to the FDA.

Federal regulators are concerned about the rise of nicotine vaping among teenagers, citing that the habit can lead to cigarette smoking. Tobacco use is a major cause of cancer and other ailments.

More recently Walmart received a letter from the FDA's then commissioner Scott Gottlieb on April 5, but the retailer challenged the violation rates that Gottlieb cited.

Last year, Walmart passed 94 percent of over 2,400 checks by the FDA, Scudder said, while Sam's Club passed each of its 15 checks. Those numbers were "significantly higher than the rates referenced in Dr. Gottlieb's April 5 letter and in our view more fairly and accurately portray our performance,'' Scudder wrote.

Walmart says that it already requires staffers who sell tobacco products to undergo training. But starting last month the company began subjecting employees who fail checks by secret shoppers to disciplinary action, which can include being fired. Such actions were previously taken only in regard to failed FDA checks.