"The alleged misrepresentation here — that 'light' and 'low-tar' cigarettes are not as healthy as advertised — is actionable only because of the effect that smoking light and low-tar cigarettes had on respondents' health," Thomas said.
Shares of Altria Group Inc. fell 17 cents, or 1.1 percent, to $15.17 in morning trading Monday while shares of rival cigarette maker Reynolds American Inc. lost 91 cents, or 2.2 percent, to $39.64.
Three Maine residents sued Altria and Philip Morris under the state's law against unfair marketing practices. The class-action claim represents all smokers of Marlboro Lights or Cambridge Lights cigarettes, both made by Philip Morris.
A federal district court threw out the lawsuit, but the 1st U.S. Circuit Court of Appeals said it could go forward.
The lawsuit argues that the company knew for decades that smokers of light cigarettes compensate for the lower levels of tar and nicotine by taking longer puffs and compensating in other ways.
David Frederick, who represented the Maine residents at the high court, said: "Had the court gone the other way, it would have been open season for the tobacco companies to continue to perpetrate fraud on the tobacco-consuming public."
The court also rejected Philip Morris' argument that the Federal Trade Commission's endorsement in the mid-1960s of machine testing of cigarette tar and nicotine levels should relieve the company of liability for alleged fraud.
Last month, the FTC formally dropped its endorsement of the test, known as the Cambridge Filter Method.
The commission said the test method is flawed because, among other things, the machine doesn't take into account the way smokers adjust their behavior.
The case is Altria Group Inc. v. Good, 07-562.
Copyright 2009 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.
Do you have more information about this topic? If so, please click here to contact the editors of ABC News.
