37 CFR § 11.307 - Practitioner as witness.
(1) The testimony relates to an uncontested issue;
(2) The testimony relates to the nature and value of legal services rendered in the case; or
(3) Disqualification of the practitioner would work substantial hardship on the client.
(b) A practitioner may act as advocate in a proceeding before a tribunal in which another practitioner in the practitioner's firm is likely to be called as a witness unless precluded from doing so by §§ 11.107 or 11.109.
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