Whether the Federal Arbitration Act permits courts, invoking the "federal substantive law of arbitrability," to invalidate arbitration agreements on the ground that they do not permit class arbitration of a federal-law claim.
In In re American Express Merchants Litigation, 667 F.3d 204 (2d Cir. 2012), the Second Circuit refused to enforce a no-class-action arbitration clause notwithstanding Concepcion because doing so would interfere with the effective vindication of the federal antitrust laws. The Supreme Court has addressed this issue in Mitsubishi Motors Corp. v. Soler Chrysler-Plymouth, Inc., 473 U.S. 614 (1985).
SCOTUSblog has a case page with links to the briefing to date, including:
The petitioners' brief on the merits will be due in 45 days, or by appproximately December 24, 2012.