Mark and Jackie Barden, whose 7-year-old son Daniel was murdered in the Sandy Hook massacre in December 2012, have voiced their opposition to comments Sen. Bernie Sanders made during a Democratic presidential debate on March 6 that gun manufacturers should not be liable if a crime is committed with their product.

In a Washington Post op-ed published online on Friday, the Bardens argued that the Bushmaster AR-15 rifle, which was used to kill their son, 19 other children and six adults in the elementary school shooting, is a highly lethal military weapon that should not be sold to the public. The parents, along with nine other families, filed a lawsuit in December 2014 against Remington Arms, which manufactured the weapon Adam Lanza used to carry out the attack in Newtown, Connecticut.

“If you go to a store and you legally purchase a gun, and three days later you go out and start killing people, is the point to hold the gun shop owner or the manufacturer of that gun liable? If that’s the point, I disagree,” Sanders said. “If they are selling a product to a person who buys it legally, what you’re talking about is ending gun manufacturing in America.”

In the op-ed, the Bardens said the Vermont senator “has spent decades tirelessly advocating for greater corporate responsibility, which is why we cannot fathom his support of companies that recklessly market and profit from the sale of combat weapons to civilians and then shrug their shoulders when the next tragedy occurs, leaving ordinary families and communities to pick up the pieces.”

The National Rifle Association posted a tweet in support of a comment the Vermont senator made on gun industry immunity during a heated exchange in Sunday night’s Democratic debate with his rival, former Secretary of State Hillary Clinton.

“Sen. Sanders was spot-on in his comments about gun manufacturer liability/PLCAA,” the gun lobby tweeted. The post was accompanied by a graphic of the senator’s remarks: “What you’re talking about is ending gun manufacturing in America. I don’t agree with that.”

During the debate, which was televised live from Flint, Michigan, host Anderson Cooper asked Sanders and Clinton if they support a lawsuit filed by families of the Sandy Hook Elementary shooting victims. The suit is against Remington Arms Company, which manufactured the weapon the gunman used. Cooper said it might not go anywhere because of a law Sanders backed in 2005 that shields gun manufacturers from certain lawsuits when someone legally buys a gun and then intentionally misuses it.

Ian Sams, a spokesman for the Clinton campaign, tweeted, “While the NRA defends @BernieSanders, it attacks @HillaryClinton. What more do we need to know?”