Walmart is voluntarily hiking the minimum age at which its customers can buy cigarettes and other tobacco products in an effort to keep them out of the hands of minors.

In a letter to the Food & Drug Administration Wednesday, the company said only those over the age of 21 will be able to buy cigarettes going forward. The ban will take effect in July and will also include its Sam's Club warehouse stores.

The chain is also discontinuing the sale of fruit and dessert-flavored e-cigarettes.

"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," wrote John Scudder, Walmart's U.S. chief compliance and ethics officer.

The retail giant says it plans to conduct numerous "secret shopper" visits to ensure the new guidelines are followed.