The fine line that the retailer is walking to address the concerns of both gun rights and gun control advocates reflects how heated the issue has become, particularly in light of recent mass shootings.

Most states allow people to openly carry licensed guns in some way and many companies do not have policies banning firearms in their stores. But Starbucks has become a target for gun control advocates, in part because of its liberal-leaning corporate image. In turn, gun rights advocates have been galvanised by the company's decision to defer to local laws.

In an interview, CEO Howard Schultz said the decision to ask customers to stop bringing guns into stores came as a result of the growing frequency of "Starbucks Appreciation Days" in recent months, in which gun rights advocates turn up at Starbucks cafes with firearms.

Last month, for example, the company closed down a store in Newtown, Connecticut, for the day after learning that gun rights advocates planned to hold a "Starbucks Appreciation Day" at the location. The store was near the school where a gunman killed 20 children and six women.

Schultz said the events mischaracterised the company's stance on the issue and the demonstrations "have made our customers uncomfortable."

Schultz hopes people will honour the request not to bring in guns but says the company will nevertheless serve those who do.

"We will not ask you to leave," he said.

The Seattle-based company plans to buy ad space in major national newspapers including The New York Times, Wall Street Journal, Washington Post and USA Today on Thursday to run an open letter from Schultz explaining the decision. The letter points to recent activities by both gun rights and gun control advocates at its stores, saying that it has been "thrust unwillingly" into the middle of the national debate over firearms.

As for the "Starbucks Appreciation Days" being staged by gun rights advocates, it stresses: "To be clear: we do not want these events in our stores."

But the letter notes that Starbucks is standing by its position that the matter should ultimately be left to lawmakers. Schultz also said he doesn't want to put workers in the position of having to confront armed customers by banning guns.

The AP was provided a picture of a memo to Starbucks employees on Tuesday. Partners are instructed not to confront customers or ask them to leave solely for carrying a weapon.

Several companies do not allow firearms in their stores, however, apparently with little trouble. Representatives for Peet's Coffee & Tea and Whole Foods, for example, said there haven't been any problems with enforcing their gun bans.

Moms Demand Action for Gun Sense in America, which was formed the day after the Newtown, Connecticut, school shooting, has been organising "Skip Starbucks Saturdays" to urge the coffee company to ban guns at its stores. Participants take photos of themselves at competitors such as Peet's that do not allow guns and post them online.

Shannon Watts, founder of the gun reform group, noted that Starbucks has taken strong stances on other issues. Earlier this year, for example, the company banned smoking within 25 feet (7.6 metres) of its stores, wherever its leases allowed. The idea was to extend its no-smoking policy to the outdoor seating areas.

"There's a big difference in the connotation of someone holding a gun and someone holding a cigarette," Schultz said.

In the meantime, Starbucks has become a symbol for advocates of gun rights. A website now even sells products bearing an altered version of the Starbucks logo, with the siren holding up a gun in each hand with the words "I Love Guns & Coffee".

AP