The US Supreme Court heard two cases that could limit the scope of class action lawsuits, after the court rejected a discrimination claim by 1.5 million female workers against retail giant Wal-Mart.
Comcast, the largest US cable operator, faces a class action lawsuit from two million of its customers in the eastern state of Pennsylvania.
The court also heard arguments in a case brought by the Connecticut Retirement Plans and Trust Funds against pharmaceutical laboratories Amgen.
The plaintiffs argued that the company artificially inflated the market price for Amgen stock by making misrepresentations about the safety of two Amgen drugs designed to stimulate red blood cell production and to reduce the need for blood transfusions.
Comcast subscribers argue that the cable company giant bought up competitors and, with control of nearly 70 percent of the market, were able to raise cable television subscription prices in the Philadelphia area.
"These actions were designed to eliminate competition, raise barriers to entry for potential competition and increase prices for services to supracompetitive levels," the plaintiff's brief read.
Comcast, however, wants the Supreme Court to reject the lawsuit because the plaintiffs as a group have not shown "a violation of the antitrust laws, individual injury resulting from that violation" or "measurable damages."
The case is further complicated by an out-of-court settlement reached between the parties in June, two weeks before the case reached the court.
The Supreme Court must say whether a lower court was correct in allowing the Comcast case to proceed, or if -- as the cable operator claims -- it should have adopted an "admissible evidence" rule attesting to common damage suffered by the plaintiffs.
"The question on damages," said Justice Stephen Breyer, "is to what extent did the absence of competition... raise price above the competitive level?"
The attorney representing the Comcast customers, Barry Barnett, said that "the only thing that's really before the court is whether it's more likely than not the plaintiffs have presented a model" demonstrating that the plaintiffs have suffered harm.
Rulings on the cases are expected next year.
In a landmark June 20, 2011 ruling, the top US court voted that since Wal-Mart had no overarching employment policy, the women that sued the company could not all have suffered discrimination for the same reasons.
The justices said the world's largest retailer should therefore not be held liable for the tens of billions of dollars in backpay and damages sought by the plaintiffs.