[What you need to know to start the day: Get New York Today in your inbox.]

The Connecticut Supreme Court dealt a major blow to the firearms industry on Thursday, clearing the way for a lawsuit against the companies that manufactured and sold the semiautomatic rifle used by the gunman in the massacre at Sandy Hook Elementary School.

The lawsuit mounted a direct challenge to the immunity that Congress granted gun companies to shield them from litigation when their weapons are used in a crime. The ruling allows the case, brought by victims’ families, to maneuver around the federal shield, creating a potential opening to bring claims to trial and hold the companies, including Remington, which made the rifle, liable for the attack.

The decision represents a significant development in the long-running battle between gun control advocates and the gun lobby. And it stands to have wider ramifications, experts said, by charting a possible legal road map for victims’ relatives and survivors from other mass shootings who want to sue gun companies.

In the lawsuit, the families seized upon the marketing for the AR-15-style Bushmaster used in the 2012 attack, which invoked the violence of combat and used slogans like “Consider your man card reissued.”