(a) Each party to the proceeding may file proposed findings of fact and conclusions, briefs, or memoranda of law: Provided, however, That the presiding officer may direct any party other than Commission counsel to file proposed findings of fact and conclusions, briefs, or memoranda of law. Such proposed findings of fact, conclusions, briefs, and memoranda of law shall be filed within 20 days after the record is closed, unless additional time is allowed.
(b) All pleadings and other papers filed pursuant to this section shall be accompanied by proof of service thereof upon all other counsel in the proceeding; if a party is not represented by counsel, proof of service upon such party shall be made.
(c) In the absence of a showing of good cause therefor, the failure to file proposed findings of fact, conclusions, briefs, or memoranda of law, when directed to do so, may be deemed a waiver of the right to participate further in the proceeding. (5 U.S.C. 557)