NY Court of Appeals addresses high low agreements.

Court holds that whenever a plaintiff and a defendant enter into a high-low agreement in a multi-defendant action which requires the agreeing defendant to remain a party to the litigation, the parties must disclose the existence of that agreement and its terms to the court and the non-agreeing defendant(s).

http://www.nycourts.gov/ctapps/decisions/jun07/89opn07.pdf