Sixteen of the world's largest banks including JPMorgan Chase & Co. and Citigroup Inc. must face antitrust lawsuits accusing them of hurting investors who bought securities tied to Libor by rigging an interest-rate benchmark, a ruling that an appeals court warned could devastate them.

The appellate judges reversed a lower-court ruling on one issue — whether the investors had adequately claimed in their complaints to have been harmed — while sending the cases back for the judge to consider another issue: whether the plaintiffs are the proper parties to sue, in part because their claims, if successful, provide for triple damages that could overwhelm the banks.

"Requiring the banks to pay treble damages to every plaintiff who ended up on the wrong side of an independent Libordenominated derivative swap would, if appellants' allegations were proved at trial, not only bankrupt 16 of the world's most important financial institutions, but also vastly extend the potential scope of antitrust liability in myriad markets where derivative instruments have proliferated," the U.S. Court of Appeals in New York said in the ruling.