Production of additional evidence: Commission may admit late evidence for substantial cause while ensuring opportunity to rebut. Parties are generally barred from producing before the Commission additional evidence that was not produced during the Director General's investigation, but the Commission may, for reasons to be recorded, allow production of documents, witness examination, or affidavits where necessary to pass orders, for substantial causes, or if opportunity to adduce evidence was inadequate. Such evidence may be taken before the Commission or a directed authority, which must forward records to the Commission, and the Commission must provide the additional evidence to other parties and permit opportunity to rebut.