28 U.S. Code § 455 – Disqualification of justice, judge, or magistrate judge
(a) Any justice, judge, or magistrate judge of the United States shall disqualify himself in any proceeding in which his impartiality might reasonably be questioned.
(b) He shall also disqualify himself in the following circumstances:
(1) Where he has a personal bias or prejudice concerning a party, or personal knowledge of disputed evidentiary facts concerning the proceeding;
(2) Where in private practice he served as lawyer in the matter in controversy, or a lawyer with whom he previously practiced law served during such association as a lawyer concerning the matter, or the judge or such lawyer has been a material witness concerning it;
https://www.law.cornell.edu/uscode/text/28/455//
Code of Conduct for United States Judges
Canon 2: A Judge Should Avoid Impropriety and the Appearance of Impropriety in all Activities
(A) Respect for Law. A judge should respect and comply with the law and should act at all times in a manner that promotes public confidence in the integrity and impartiality of the judiciary.
(B) Outside Influence. A judge should not allow family, social, political, financial, or other relationships to influence judicial conduct or judgment. A judge should neither lend the prestige of the judicial office to advance the private interests of the judge or others nor convey or permit others to convey the impression that they are in a special position to influence the judge. A judge should not testify voluntarily as a character witness.
(C) Nondiscriminatory Membership. A judge should not hold membership in any organization that practices invidious discrimination on the basis of
race, sex, religion, or national origin.
http://www.uscourts.gov/judges-judgeships/code-conduct-united-states-judges
