The complainant and the respondent will be parties in every proceeding and must be served with copies of all documents in the case. At the Assistant Secretary's discretion, the Assistant Secretary may participate as a party or as amicus curiae at any time at any stage of the proceeding. This right to participate includes, but is not limited to, the right to petition for review of a decision of an ALJ, including a decision approving or rejecting a settlement agreement between the complainant and the respondent.

Parties must send copies of documents to OSHA and to the Associate Solicitor, Division of Fair Labor Standards, U.S. Department of Labor, only upon request of OSHA, or when OSHA is participating in the proceeding, or when service on OSHA and the Associate Solicitor is otherwise required by these rules.

The Department of Homeland Security or the Department of Transportation, if interested in a proceeding, may participate as amicus curiae at any time in the proceeding, at those agencies' discretion. At the request of the interested federal agency, copies of all documents in a case must be sent to the federal agency, whether or not the agency is participating in the proceeding.