In a 5-4 split won by the court's liberals, it ruled that smokers may use state consumer protection laws to sue cigarette makers for the way they promote "light" and "low tar" brands.
The decision was at odds with recent anti-consumer rulings that limited state regulation of business in favor of federal power.
Altria Group Inc. argued on behalf of its Philip Morris USA subsidiary that the lawsuits are barred by the federal cigarette labeling law, which forbids states from regulating any aspect of cigarette advertising that involves smoking and health.
Justice John Paul Stevens, however, said in his majority opinion that the labeling law does not shield the companies from state laws against deceptive practices. The decision forces tobacco companies to defend dozens of suits filed by smokers in Maine, where the case originated, and across the country.