"Because the plaintiffs here have not nudged their claims across the line from conceivable to plausible, their complaint must be dismissed," Justice David Souter wrote in the 7-2 majority opinion.
The ruling reversed a lower court ruling that let a lawsuit proceed against Bell Atlantic Corp., BellSouth Corp., Qwest Communications International Inc. and SBC Communications Inc.
Bell Atlantic is now Verizon Communications Inc. and SBC bought AT&T Inc., renaming the company AT&T before merging with BellSouth.
The case alleged the phone companies engaged in an anticompetitive conspiracy to restrict local telephone and broadband-Internet competition.
The companies and the U.S. Justice Department had asked the court to set private antitrust-lawsuit standards high enough to stop expensive legal discovery in cases with questionable merit.
Justice John Paul Stevens and Ruth Bader Ginsburg dissented, saying the case should have at least been allowed to proceed to the discovery pre-trial phase. In that phase, each party can request documents and other evidence from other parties or compel the release of evidence by subpoena and other means.