The representative authorized to withdraw or annul a certificate under § 528.3 shall institute proceedings by a letter mailed to the employer and, where appropriate, to the apprenticeship agency (in the case of apprentice certificates) or the responsible school official (in the case of student-learner certificates), setting forth alleged facts which may warrant such annulment or withdrawal and advising the employer that such an annulment or withdrawal of the scope provided in § 528.7 will take effect at a time specified unless facts are presented which convince the authorized representative that such action should not be taken. The letter shall advise such person, agency, or official of the right to respond by mail or to appear by or with counsel or by other duly qualified representative at a specified time and place. If there is no timely objection to the withdrawal or annulment thus proposed, it shall be deemed effective according to the terms of the letter instituting the annulment or withdrawal proceeding without the necessity of any further action. If objection to the annulment or withdrawal as proposed is made within the specified time the further proceedings shall be as informal as practicable commensurate with orderly dispatch and fairness. Department of Labor investigation files or reports or portions thereof may be considered in such proceedings to the extent they are made available for examination during the proceedings. If objection to the proposed annulment or withdrawal is made by such specified time, the authorized representative shall, after considering all pertinent matters presented, mail a letter to the employer and, where appropriate, to the apprenticeship agency or the responsible school official, setting out that representative's findings of specific pertinent facts and conclusions and that representative's order concerning the proposed annulment or withdrawal. In proceedings instituted for annulment, the order may provide for withdrawal instead of annulment if the proof warrants such withdrawal but fails to support adequately the annulment. Such an order shall be deemed issued and effective according to its terms when mailed.