; or (B) the date on which such miner, employee, representative, or applicant 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 a complaint under paragraph (2), the Secretary shall— (i) forward a copy of the complaint to the respondent; (ii) commence an investigation within 15 days of the Secretary’s receipt of the complaint; and (iii) as soon as practicable after commencing the investigation under clause (ii), make the determination required under subparagraph (B). (B) Reinstatement If the Secretary finds that a complaint under paragraph (2) was not frivolously brought, the Commission, on an expedited basis upon application of the Secretary, shall order the immediate reinstatement of the miner, employee, or representative described in such paragraph until there has been a final Commission order disposing of the underlying complaint. If either the Secretary or such miner, employee, or representative 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 such miner, employee, or representative 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