The Commission may conduct audits and field investigations of any political committee required to file a report under section
434 of this title. All audits and field investigations concerning the verification for, and receipt and use of, any payments received by a candidate or committee under chapter
95 or chapter
96 of title
26 shall be given priority. Prior to conducting any audit under this subsection, the Commission shall perform an internal review of reports filed by selected committees to determine if the reports filed by a particular committee meet the threshold requirements for substantial compliance with the Act. Such thresholds for compliance shall be established by the Commission. The Commission may, upon an affirmative vote of 4 of its members, conduct an audit and field investigation of any committee which does meet the threshold requirements established by the Commission. Such audit shall be commenced within 30 days of such vote, except that any audit of an authorized committee of a candidate, under the provisions of this subsection, shall be commenced within 6 months of the election for which such committee is authorized.