Paul Stern argued that his state, like many others, is trying to keep tobacco from underage smokers and that cannot be done without the help of companies that deliver cigarettes bought over the Internet.

Congress has encouraged the states "to deal with the significant public health problem of youth access to tobacco," Stern told the court, arguing for Maine's right to regulate shipment of cigarettes bought online.

Shipping industry associations that are challenging the law object to delivery requirements that they say only the federal government can impose.

Federal law bars states from regulating prices, routes or services of shipping companies and Maine's law "certainly relates to the service" of the shipping companies, Chief Justice John Roberts said.

"It talks about what carriers have to do," Roberts added.

Recent research says children as young as age 11 were successful more than 90 percent of the time in buying cigarettes over the Internet. At last count, there were 772 Internet cigarette vendors, a nearly nine-fold increase in seven years, according to Kurt Ribisl, an associate professor at the University of North Carolina's school of public health who has spent the past eight years studying the issue.

In 2002, at the start of the boom in Internet cigarette sites, a study found that Internet vendors sold 400 million packs of cigarettes a year, 2 percent of the cigarettes consumed in the United States and a figure that anti-smoking groups say is growing.

The case also involves the issue of uncollected state taxes. One study found that three-quarters of Internet tobacco sellers say they will not report cigarette sales to tax collection officials. A private research firm found states lose as much as $1.4 billion annually in uncollected tobacco taxes through Internet sales.

The lost revenue is a concern to Maine and about 40 other states that have tried to prohibit or severely restrict the direct delivery of tobacco products to consumers.

The differences in the state laws are a burden to business, several justices suggested.

"What if every state enacted a slightly different law relating to this and a slightly different law relating to every other product that they might want to restrict for health or safety reasons?" asked Justice Samuel Alito.

Justice Stephen Breyer said it would be a "nightmare" if every state were to pass a different law on what it takes to prove that a shipping company knowingly delivered an unlicensed product.

To Justice David Souter, the federal ban on state regulation of interstate shipping was intended "to end the economic effects of state patchwork transportation regulation."

If Maine's tobacco delivery law is not tossed out, "there will be different delivery laws in states across the country, and that patchwork will eliminate the efficiency and the cost savings that was Congress' intent," said lawyer Beth Brinkmann, arguing for the transportation associations.

Maine says delivery companies must check packages against a list from the state of known unlicensed tobacco retailers. The shipping companies must deliver only to the person to whom the package is addressed and a recipient under 27 must present identification before the package can be delivered.

Facing legal trouble in New York state in 2005, United Parcel Service Inc. agreed to stop shipping cigarettes to individual consumers in all 50 states. The company says it did so because of the varying state laws. FedEx and DHL have signed similar agreements.

Two lower federal courts have rejected Maine's law. The Supreme Court is expected to rule in the case by next June.

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