Ex Parte Communication

Ex parte (Latin: "from one party") communications are contacts between a party (or its lawyer) and a judge, arbitrator, or administrative adjudicator concerning a pending case without the other side being present or notified. Because adversarial systems rest on the principle that both sides hear and can rebut everything the decision-maker considers, such contacts are presumptively improper.

In the United States, the prohibition is codified in Rule 3.5 of the ABA Model Rules of Professional Conduct for lawyers and Canon 3(A)(4) of the Code of Conduct for United States Judges for the bench. Federal agency adjudications are governed by the Administrative Procedure Act, 5 U.S.C. § 557(d), which bars off-the-record contacts with agency decision-makers in formal proceedings and requires disclosure on the public record if they occur. Similar rules appear in most state judicial codes and in the procedural rules of international tribunals, including the ICSID and ICC arbitration rules.

Not every one-sided contact is forbidden. Recognized exceptions typically include:

• Scheduling, administrative, or emergency matters that do not address the merits.
• Statutorily authorized applications, such as requests for temporary restraining orders, search warrants, or wiretap authorizations, where notice would defeat the purpose of the relief.
• Settlement or mediation conferences where the neutral meets separately with each side by agreement (caucusing).

Consequences for improper ex parte contact can include disqualification of the judge, vacatur of the resulting order, professional discipline for the lawyer, and in agency settings, the contact being placed on the public record. The doctrine intersects with broader due process guarantees — for example, the U.S. Supreme Court in Caperton v. A.T. Massey Coal Co. (2009) addressed when undisclosed influence on a judge violates the Due Process Clause, reinforcing the transparency norms that ex parte rules protect.