The U.S. Supreme Court heard argument in a particularly interesting and (I think) important case today. In Hall Street Associates, L.L.C. v. Mattel, Inc. (06-989), the Court will decide whether contracting parties may agree to expand the grounds for vacating arbitration awards beyond those recognized under the Federal Arbitration Act. The Fifth Circuit and others have said yes—seeGateway Techs., Inc. v. MCI Telecomms. Corp., 64 F.3d 993 (5th Cir. 1995)—but the Ninth Circuit disagreed. The merits briefs, amicus briefs, and a transcript of the argument are available here.