American Bar Association Model Rules of Professional Conduct - Rule 8.5. Disciplinary Authority; Choice of Law
(a) Disciplinary Authority. A lawyer admitted to practice in this jurisdiction is subject to the disciplinary authority of this jurisdiction, regardless of where the lawyer's conduct occurs. A lawyer not admitted in this jurisdiction is also subject to the disciplinary authority of this jurisdiction if the lawyer provides or offers to provide any legal services in this jurisdiction. A lawyer may be subject to the disciplinary authority of both this jurisdiction and another jurisdiction for the same conduct.
(b) Choice of Law. In any exercise of the disciplinary authority of this jurisdiction, the rules of professional conduct to be applied shall be as follows:
(1) for conduct in connection with a matter pending before a tribunal, the rules of the jurisdiction in which the tribunal sits, unless the rules of the tribunal provide otherwise; and
(2) for any other conduct, the rules of the jurisdiction in which the lawyer's conduct occurred, or, if the predominant effect of the conduct is in a different jurisdiction, the rules of that jurisdiction shall be applied to the conduct. A lawyer shall not be subject to discipline if the lawyer's conduct conforms to the rules of a jurisdiction in which the lawyer reasonably believes the predominant effect of the lawyer's conduct will occur.