; or (B) the date on which the miner or other employee or representative knows or should reasonably have known that such alleged violation occurred. (3) Investigation and hearing (A) Commencement of investigation and initial determination Upon receipt of such complaint, the Secretary shall forward a copy of the complaint to the respondent, and shall commence an investigation within 15 days of the Secretary’s receipt of the complaint, and, as soon as practicable after commencing such investigation, make the determination required under subparagraph (B) regarding the reinstatement of the miner or other employee. (B) Reinstatement If the Secretary finds that such complaint was not frivolously brought, the Commission, on an expedited basis upon application of the Secretary, shall order the immediate reinstatement of the miner or other employee until there has been a final Commission order disposing of the underlying complaint of the miner or other employee. If either the Secretary or the miner or other employee pursues the underlying complaint, such reinstatement shall remain in effect until the Commission has disposed of such complaint on the merits, regardless of whether the Secretary pursues such complaint by filing a complaint under subparagraph (D) or the miner or other employee pursues such complaint by filing an action under paragraph (4). If neither the Secretary nor the miner or other employee pursues the underlying complaint within the periods specified in paragraph (4), such reinstatement shall remain in effect until such time as the Commission may, upon motion of the operator and after providing notice and an opportunity to be heard to the parties, vacate such complaint for failure to prosecute. (C) Investigation Such investigation shall include interviewing the complainant and— (i) providing the respondent an opportunity to submit to the Secretary a written response to the complaint and to present statements from witnesses or provide evidence