29 C.F.R. § 1903.12

(a) If the Area Director determines that an inspection is not warranted because there are no reasonable grounds to believe that a violation or danger exists with respect to a complaint under § 1903.11, he shall notify the complaining party in writing of such determination. The complaining party may obtain review of such determination by submitting a written statement of position with the Assistant Regional Director and, at the same time, providing the employer with a copy of such statement by certified mail. The employer may submit an opposing written statement of position with the Assistant Regional Director and, at the same time, provide the complaining party with a copy of such statement by certified mail. Upon the request of the complaining party or the employer, the Assistant Regional Director, at his discretion, may hold an informal conference in which the complaining party and the employer may orally present their views. After considering all written and oral views presented, the Assistant Regional Director shall affirm, modify, or reverse the determination of the Area Director and furnish the complaining party and the employer and written notification of this decision and the reasons therefor. The decision of the Assistant Regional Director shall be final and not subject to further review.

(b) If the Area Director determines that an inspection is not warranted because the requirements of § 1903.11(a) have not been met, he shall notify the complaining party in writing of such determination. Such determination shall be without prejudice to the filing of a new complaint meeting the requirements of § 1903.11(a).