37 CFR §11.107

1. (a)Except as provided in paragraph (b) of this section, a practitioner shall not represent a client if the representation involves a concurrent conflict of interest. A concurrent conflict of interest exists if:
   1. (1)The representation of one client will be directly adverse to another client; or
   2. (2)There is a significant risk that the representation of one or more clients will be materially limited by the practitioner's responsibilities to another client, a former client or a third person or by a personal interest of the practitioner.
2. (b)Notwithstanding the existence of a concurrent conflict of interest under paragraph (a) of this section, a practitioner may represent a client if:
   1. (1)The practitioner reasonably believes that the practitioner will be able to provide competent and diligent representation to each affected client;
   2. (2)The representation is not prohibited by law;
   3. (3)The representation does not involve the assertion of a claim by one client against another client represented by the practitioner in the same litigation or other proceeding before a tribunal; and
   4. (4)Each affected client gives informed consent, confirmed in writing.