WASHINGTON — The U.S. Supreme Court dealt a blow to the gun industry, refusing to block a lawsuit against Remington Arms Co. by family members of nine people killed in the 2012 Sandy Hook Elementary School massacre.

The lawsuit blames the gunmaker’s marketing practices for inspiring the killer, Adam Lanza, who used a Remington-made Bushmaster XM15 military-style rifle while killing 26 people at the Connecticut school, 20 of them first-grade children.

The justices rejected Remington’s appeal Tuesday without comment or published dissent. The rebuff leaves intact a Connecticut Supreme Court ruling that carved a way around a 2005 federal law enacted to shield the gun industry from lawsuits. Gun-rights advocates including the National Rifle Association had urged the high court to hear Remington’s appeal.

The Connecticut court decision “threatens to unleash a flood of lawsuits nationwide that would subject lawful business practices to crippling litigation burdens,” Remington argued in its appeal.

The families said in court papers that Remington “chose to market the XM15-E2S as a highly lethal weapon designed for purposes that are illegal — namely, killing other human beings.”

The Supreme Court’s decision to let the suit go forward could give the families access to company documents and internal communications, information that could help others seeking to press similar suits.

The 2005 Protection of Lawful Commerce in Arms Act insulates gun manufacturers and merchants but makes an exception if a company has “knowingly violated a state or federal statute applicable to the sale or marketing of the product.”

Remington said the clause, known as the “predicate exception,” covers only laws that explicitly regulate the firearms business, not general consumer-protection statutes like the Connecticut law.

“The Connecticut Supreme Court gave the predicate exception such a broad reading that it threatens to swallow the PLCAA’s immunity rule,” the company argued.

The Connecticut court said in a 4-3 vote that the exception lets the families sue over Remington’s marketing practices under Connecticut’s unfair trade practices law.

“If Congress had intended to limit the scope of the predicate exception to violations of statutes that are directly, expressly, or exclusively applicable to firearms, however, it easily could have used such language, as it has on other occasions,” said the majority opinion.

The Supreme Court’s refusal to hear the case lets it sidestep a divisive and emotional clash. The justices are already scheduled to hear one gun case, a fight scheduled for argument Dec. 2 over New York restrictions on where handguns can be taken.