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.”

Lawyers for the families argued that those messages reflected a deliberate effort to appeal to troubled young men like Adam Lanza, the 20-year-old who charged into the elementary school and killed 26 people, including 20 first graders, in a spray of gunfire. The attack traumatized the nation and made Newtown, Conn., the small town where it happened, a rallying point in the broader debate over gun violence.

In the 4-3 ruling, the justices agreed with a lower court judge’s decision to dismiss most of the claims raised by the families, but also found that the sweeping federal protections did not prevent the families from bringing a lawsuit based on wrongful marketing claims. The court ruled that the case can move ahead based on a state law regarding unfair trade practices.

In the majority opinion, the justices wrote that “it falls to a jury to decide whether the promotional schemes alleged in the present case rise to the level of illegal trade practices and whether fault for the tragedy can be laid at their feet.”

The families hailed the ruling as a victory. “I am thrilled and tremendously grateful,” said Nicole Hockley, whose 6-year-old son Dylan was killed in his first-grade classroom. “No one has blanket immunity. There are consequences. We want our day in court to see why they do this this way, and what needs to change.”