NEW YORK — Dick’s Sporting Goods will immediately stop selling assault-style rifles and ban the sale of all guns to anyone under 21, the company said Wednesday, as its CEO took on the National Rifle Association by demanding tougher gun laws after the massacre in Florida.

The strongly worded 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, “ Chairman and CEO Ed Stack said on ABC’s  “Good Morning America. “

The change in sales practices, and the emphatic words from Stack, put Dick’s out front in the falling-out between corporate America and the gun lobby. Several major corporations, including MetLife, Hertz and Delta Air Lines, have cut ties with the NRA since the Florida tragedy, but until now, none were retailers that sold guns.

The announcement drew hundreds of thousands of responses for and against on the company’s Facebook page.

Dick Sporting Goods had cut off sales of assault-style weapons after the 2012 Sandy Hook Elementary School shooting. But sales had resumed at its smaller chain of Field & Stream stores, which consisted of 35 outlets in 16 states as of October.

On Wednesday, Stack said that would end, and he called on lawmakers to act now.

He urged them to ban assault-style firearms, bump stocks and high-capacity magazines and raise the minimum age to buy firearms to 21. He said universal background checks should be required, and there should be a complete database of those banned from buying firearms. He also called for the closing of the private sale and gun show loophole that enables purchasers to escape background checks.

“We support and respect the Second Amendment, and we recognize and appreciate that the vast majority of gun owners in this country are responsible, law-abiding citizens, “ Stack said in a letter.  “But we have to help solve the problem that’s in front of us. Gun violence is an epidemic that’s taking the lives of too many people, including the brightest hope for the future of America — our kids. “

The NRA has pushed back aggressively against calls for raising age limits for guns or restricting the sale of assault-style weapons. Calls to the NRA were not immediately returned.

Stack also revealed 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 is selling sporting goods like basketballs and sneakers. Joseph Feldman, a senior managing director at the Telsey Advisory Group, estimates that the hunting category — which includes guns — accounts for 8 percent to 10 percent of the company’s sales.

Dick’s, which had net sales of $7.92 billion in the fiscal year that ended in January 2017, has a much bigger stake in youth sports “The longer-term positive perception that they create a more welcoming environment will offset any lost sales in the year, “ Feldman said.