The Board may, in its discretion, require the parties to submit prehearing briefs in any case in which a hearing has been elected under the regular procedure. (Rule 8(a)(1)). If the Board does not ask for briefs, either party may, upon notice to the other party, furnish a prehearing brief to the Board. In any case where a prehearing brief is submitted, it shall be furnished so as to be received by the Board at least 15 days prior to the date set for hearing, and a copy shall be furnished simultaneously to the other party.