37 CFR §11.109

1. (a)A practitioner who has formerly represented a client in a matter shall not thereafter represent another person in the same or a substantially related matter in which that person's interests are materially adverse to the interests of the former client unless the former client gives informed consent, confirmed in writing.
2. (b)A practitioner shall not knowingly represent a person in the same or a substantially related matter in which a firm with which the practitioner formerly was associated had previously represented a client:
   1. (1)Whose interests are materially adverse to that person; and
   2. (2)About whom the practitioner had acquired information protected by §§ 11.106 and 11.109(c) that is material to the matter; unless the former client gives informed consent, confirmed in writing.
3. (c)A practitioner who has formerly represented a client in a matter or whose present or former firm has formerly represented a client in a matter shall not thereafter:
   1. (1)Use information relating to the representation to the disadvantage of the former client except as the USPTO Rules of Professional Conduct would permit or require with respect to a client, or when the information has become generally known; or
   2. (2)Reveal information relating to the representation except as the USPTO Rules of Professional Conduct would permit or require with respect to a client.