In a unanimous decision, the court said Wednesday that Maine cannot impose a regulatory scheme on transportation companies delivering tobacco products directly to consumers. The justices said federal transportation law blocks the states from doing so.
The ruling could provide the impetus for the transportation industry to get out from under state laws regulating cigarette deliveries in the Internet age.
"Despite the importance of the public health objective, we cannot agree" with Maine's approach, Justice Stephen Breyer wrote.
Federal law bars states from regulating prices, routes or services of shipping companies.
Thirty-one states besides Maine have cigarette delivery laws targeting the problem of underage smokers.
Maine's law requires delivery companies to intercept packages from unlicensed tobacco sellers and to verify the age of buyers, hitting delivery companies with huge additional costs, the industry says.
Maine passed the law to ensure state tax collections and to keep cigarettes out of the hands of youths under the age of 18.