29 C.F.R. § 2204.303
The application shall be accompanied by adequate documentation of the fees and other expenses incurred after the initiation of the adversary adjudication, including, but not limited to, the reasonable cost of any study, analysis, engineering report, test, or project. An application seeking an increase in fees to account for inflation pursuant to § 2200.406 of this chapter shall also include adequate documentation of the change in the consumer price index for the attorney or agent's locality. With respect to a claim for fees and expenses involving an excessive demand by the Secretary, the application shall be accompanied by adequate documentation of such fees and expenses incurred after initiation of the adversary adjudication for which an award is sought attributable to the portion of the demand alleged to be excessive and unreasonable. A separate itemized statement shall be submitted for each professional firm or individual whose services are covered by the application, showing the hours spent in connection with the proceeding by each individual, a description of the specific services performed, the rate at which each fee has been computed, any expenses for which reimbursement is sought, the total amount claimed, and the total amount paid or payable by the applicant or by any other person or entity for the services provided. The judge or Commission may require the applicant to provide vouchers, receipts, or other substantiation for any fees or expenses claimed.
29 C.F.R. §2204.303