In addition to Bushmaster, the defendants are firearm distributor Camfour and Riverview Gun Sales, the East Windsor store where the gunman's mother purchased the Bushmaster rifle in 2010.
Messages seeking comment from the defendants were not immediately returned.
Bill Sherlach, whose wife, Mary, was killed in the shooting, said he believes in the Second Amendment but also that the gun industry needs to be held to "standard business practices" when it comes to assuming the risk for producing, making and selling a product.
"These companies assume no responsibility for marketing and selling a product to the general population who are not trained to use it nor even understand the power of it," he said.
The plaintiffs include Sherlach and the families of Vicki Soto, Dylan Hockley, Noah Pozner, Lauren Rousseau, Benjamin Wheeler, Jesse Lewis, Daniel Barden, Rachel D'Avino and teacher Natalie Hammond, who was injured in the shooting.
The lawsuit seeks unspecified monetary damages.
The Sandy Hook killer, Adam Lanza, shot dead his mother, Nancy Lanza, on the morning of Dec. 14, 2012, before driving to the school in Newtown and gunning down 20 children and six educators with the semi-automatic rifle. He committed suicide as police arrived.
In 2005, Congress and President George W. Bush approved a law that made it difficult for victims of gun violence to file lawsuits against the gun industry.
The Protection of Lawful Commerce in Arms Act (PLCAA) provides broad immunity to the gun industry and bars civil actions which result from the "criminal or lawful misuse” of firearms, according to the Law Center to Prevent Gun Violence.
The legislation, however, makes a few exceptions including a key provision that allows gun manufacturers and sellers to be held liable when they know they are breaking a federal or state law.
In the light of a spate of mass killings in recent years, some anti-gun advocates have called on the Obama administration, which has stood by the law, to repeal the PLCAA altogether. “We hope they will change their view on the constitutionality of a federal law that effectively rewrites state’s civil justice laws to protect one industry,” Jonathan Lowy, a lawyer with the Brady Center to Prevent Gun Violence told the New York Times.
Al Jazeera and The Associated Press