Dick's Sporting Goods will immediately stop selling assault-style rifles and ban the sale of all guns to anyone under 21, according to CEO Edward Stack.
The announcement from the nationwide store chain came as students at Marjory Stoneman Douglas High School in Parkland, Florida, returned to class for the first time since a teenager killed 17 students and educators with an AR-15 rifle two weeks ago.
"When we saw what the kids were going through and the grief of the parents and the kids who were killed in Parkland, we felt we needed to do something," Stack said on ABC's "Good Morning America."
In at least one Pittsburgh-area store, several customers said they support the new policies. A few who came to the Homestead location said they came because of them, like Linda Ehrenreich of Point Breeze.
Ehrenreich said she's not anti-gun; her son-in-law is a gun owner.
"There's so little we can do it seems, but if we vote with our pocketbook, that's something we can do," she said.
Mike Schneider, who lives in Squirrel Hill, said he doesn't personally own any weapons but respects the Second Amendment and believes responsible people should be able to own a handgun if they want.
"It's going to be interesting to see how it affects Dick's business," Schneider said. "Personally, I think they did the right things. Assault rifles don't need to be in the hands of minors."
Brentwood resident Mike Zahorchak said he owns an AK-47, and he likes AR-15s, "but I'd give any one of them up if I could take one of those [Parkland] kids and save their life."
One man at the Homestead branch did say he'd no longer shop at Dick's properties because of the new policy, but declined to give his name.
Dick's CEO Stack revealed during his announcement that Nikolas Cruz, the 19-year-old arrested in the Florida attack, had bought a shotgun at a Dick's store within the past four months.
"It was not the gun, nor type of gun, he used in the shooting," the CEO wrote. "But it could have been. Clearly this indicates on so many levels that the systems in place are not effective to protect our kids and our citizens."
The vast majority of Dick's business stems from sporting goods sales like basketballs and sneakers.
The Associated Press contributed to this report.