Stack acknowledged that the Parkland school shooter had purchased a shotgun at one of the company's stores in November. Though the killer did not use the gun in the shooting, the realization served as a catalyst for action.
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"We did everything by the book, we did everything that the law required and still he was able to buy a gun," Stack said. "When we looked at that, we said, 'The systems that are in place across the board just aren't effective enough to keep us from selling someone a gun like that.'"
Stack described the company's move as a direct response to the Parkland students who have pushed for change following the shooting. He said the company remains a "staunch" supporter of Second Amendment rights, adding that he owns a gun himself.
The move comes as businesses are coming under pressure to cut ties to the gun-rights lobby. Several major companies have cut discounts for members of the National Rifle Association, including Delta Air Lines, United Airlines, Enterprise, Avis Budget, Hertz, TrueCar, MetLife and Symantec.
Asked whether Dick's is prepared for a backlash, Stack said yes.
"We know that this isn't going to make everyone happy but when we take a look at what those kids and the parents and the heroes in the school, what they did, our view was if the kids can be brave enough to organize like they this, we can be brave enough to take these out of here," Stack said.
The company also took the unusual step of calling for Congress to ban assault weapons, raise the minimum wage to purchase a gun to 21 and outlaw sales of high-capacity magazines and bump stocks.
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The retailer asked Congress to impose "universal background checks" and "ensure a complete universal database of those banned from buying firearms."
"We hope others join us in this effort to let our kids know that their pleas are being taken seriously," Stack said in his open letter.
One immediate question: Will Dick's competitors follow suit?
Walmart banned assault weapons in 2015. It was not immediately clear if the company still sells guns to people under 21 or if it sells high-capacity magazines. A spokesperson was not immediately available for comment Thursday.
Cabela's and Bass Pro Shops, which are now the same company, continue to sell assault weapons and high-capacity magazines.
Representatives of Cabela's and Bass Pro Shops were not immediately available for comment.
Dick's Sporting Goods investors did not appear to be concerned by the financial implications of the decision. The company's stock barely budged in pre-market trading Thursday.