The complaint, filed on behalf of William Twombly and Lawrence Marcus, alleged that the companies refused to provide sufficient assistance to new competitors under FCC regulations. They also claimed that the firms refrained from "meaningful," but not total, competition in one another's territories.

The 2nd U.S. Circuit Court of Appeals previously ruled that allegations of companies acting similarly, combined with a conclusory allegation of conspiracy, is almost always enough to justify an antitrust claim. Justice David Souter wrote the high court's 7-2 majority opinion reversing the decision, saying it distorted basic antitrust policies.

Chief Justice John Roberts and Justices Samuel Alito, Stephen Breyer, Anthony Kennedy, Antonin Scalia and Clarence Thomas joined the majority.

Justice John Paul Stevens filed a dissenting opinion, which Ruth Bader Ginsburg supported in part. Stevens said he disagreed with the district court's dismissal of the case because it did not require a response from the Bells, which is required by federal law and prior rulings.

The ruling "embraces an important principle about protecting the freedom of firms to make unilateral decisions on what markets to enter or not enter," Verizon Deputy General Counsel John Thorne said in a statement. The decision "affirms the freedom to decide when and how to enter new markets."

Stephen McCullough, Virginia's deputy solicitor general called the ruling a "victory for common sense." Jones Day partner John Majoras said the ruling is a "death knell" for civil antitrust claims that allege a litany of parallel business activities among competitors accompanied by "an all-encompassing, yet unsupported, charge that a conspiracy lurks behind them."

He said money spent defending those cases and paying settlements that "result from the fear of unsophisticated juries being handed a treble damages bludgeon" harm the consumers that class-action lawyers purport to protect.

The U.S. Chamber of Commerce, legal scholars, economists and 16 state attorneys general filed friend-of-the-court briefs on behalf of the telephone companies. The American Antitrust Institute backed the class-action.

AAI President Albert Foer had not yet read the opinion but said it would be important to gauge "how far it may go in limiting the ability of plaintiffs to obtain discovery against cartels." A "Catch-22" could eliminate compensation of injured parties except in "follow-on" cases where the government has established a violation of law, he said.