37 C.F.R. § 2.38
(b) The Office may require such details concerning the nature of the relationship and such proofs as may be necessary and appropriate for the purpose of showing that the use by related companies inures to the benefit of the applicant and does not affect the validity of the mark.
(Sec. 5, 60 Stat. 429; 15 U.S.C. 1055)
[30 FR 13193, Oct. 16, 1965, as amended at 54 FR 37589, Sept. 11, 1989; 64 FR 48920, Sept. 8, 1999; 80 FR 2310, Jan. 16, 2015]