(a) Within 20 days of the date of service of a copy of the petition for certification, the employer shall file with the regional office an alphabetical list, including job titles or classifications, of the employees employed in the claimed unit as of the last date of the payroll period immediately preceding the date the petition was filed, unless otherwise directed by the Board.

(b) If after initial determination the proof of support is insufficient, the Board may allow up to 10 days to perfect the proof of support.

(c) Upon completion of the review of the proof of support, the Board shall inform the parties in writing of the final determination as to sufficiency or lack thereof regarding the proof of support. The petition shall be dismissed if the Board determines that the petition lacks sufficient proof of support.