The Supreme Court on Wednesday invalidated parts of Maine's law barring Internet tobacco sales to minors.

In a unanimous decision, the court said 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.

Breyer wrote that federal law "says nothing about a public health exception" enabling state regulation.

Federal law bars states from regulating prices, routes or services of shipping companies.

Because of Maine's regulation, companies will have to offer tobacco delivery services "that differ significantly" from what the market might dictate, Breyer wrote.

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.

The state of Maine argued that federal law does not pre-empt state regulation for public health and safety. The 1st U.S. Circuit Court of Appeals in Boston disagreed, rejecting Maine's argument that the federal law trumps state law only when it comes to traditional economic regulation of carriers.

The Bush administration sided with the delivery companies, declaring that when Congress deregulated the transportation industry, it determined that states should not step in to fill the void.

Congress deregulated truckers to put them on the same competitive footing with the deregulated airline industry.

The delivery companies are fighting Maine's law at the same time the industry's biggest players have stopped shipping cigarettes directly to consumers from illegal Internet sellers. The largest companies agreed to do so in the face of an aggressive campaign by the state of New York.

The ruling against Maine's law could enable the industry to argue that similar laws in other states are invalid. The decision could clear the way for companies to challenge the New York law and the agreements.

The case is Rowe v. New Hampshire Motor Transport Association, 06-457.