; vice-chairperson At the initial meeting of the Commission, the Commission shall select a Chairperson and a Vice-Chairperson from among its members. The Chairperson and Vice-Chairperson may not be members of the same political party. (d) Quorum; vacancies (1) Quorum Six members of the Commission shall constitute a quorum. (2) Vacancies Any vacancy in the Commission shall not affect the power and duties of the Commission and shall be filled in accordance with subsection (a) not later than 90 days after the occurrence of such vacancy. 4. Powers of the Commission (a) In general (1) Meetings After its initial meeting under section 3(c)(1), the Commission shall meet upon the call of the Chairperson or a majority of its members. (2) Hearings and evidence The Commission may— (A) hold such hearings, sit and act at such times and places, take such testimony, receive such evidence, including classified testimony, evidence, and information, and administer such oaths as may be necessary to carry out its functions under section 2; and (B) require, by subpoena or otherwise, the attendance and testimony of such witnesses and the production of such books, records, correspondence, memoranda, papers, and documents, including classified materials, as the Commission or such designated subcommittee or designated member may determine advisable to carry out such functions. (3) Subpoenas (A) Issuance (i) In general A subpoena may be issued under this subsection only by the agreement of the Chairperson and the Vice-Chairperson or by the affirmative vote of 5 members of the Commission. (ii) Signature Subpoenas issued under this subsection— (I) may be issued under the signature of the Chairperson or any member designated by a majority of the Commission