The justices, citing need for unfettered interstate commerce, say delivery companies cannot be required to verify that tobacco recipients are over 18.
States cannot require shipping companies to verify the age of recipients before delivering tobacco products to a home address.
The US Supreme Court on Wednesday struck down key portions of a Maine state law aimed at preventing minors from purchasing cigarettes and other tobacco products over the Internet or through other mail-order services. The vote was 9-0.
At issue was whether the 2003 state law was preempted by federal efforts to deregulate the shipping industry nationwide.
In agreeing with the shipping companies, the high court said Maine's law, while well intentioned, interfered with a congressional determination to prevent shipping companies from becoming mired in conflicting state regulations. Instead, Congress sought to leave it to the competitive marketplace to determine which services companies might offer or decline to offer.
"To allow Maine to insist that the carriers provide a special checking system would allow other states to do the same," writes Justice Stephen Breyer in the court's 11-page decision. "To interpret the federal law to permit these, and similar, state requirements could easily lead to a patchwork of state service-determining laws, rules, and regulations."
At least 39 states restrict the sale of tobacco over the Internet as a means to prevent minors from buying cigarettes. Some states ban Internet cigarette sales entirely, while others, like Maine, have tried to confine the sales to adults.