39 C.F.R. § 955.21
Hearings shall be as informal as may be reasonable and appropriate under the circumstances. The Board may exclude evidence to avoid unfair prejudice, confusion of the issues, undue delay, waste of time, or presentation of irrelevant, immaterial or cumulative evidence. Although the Board will consider the Federal Rules of Evidence as described in § 955.14(d) , letters or copies thereof, affidavits, or other evidence not ordinarily admissible under the Federal Rules, may be admitted in the discretion of the Board. The weight to be attached to evidence presented in any particular form will be within the discretion of the Board, taking into consideration all the circumstances of the particular case. Stipulations of fact agreed upon by the parties may be accepted as evidence at the hearing. The parties may stipulate the testimony that would be given by a witness if the witness were present. The Board may in any case require evidence in addition to that offered by the parties. A party requiring the use of a foreign language interpreter allowing testimony to be taken in English for itself or witnesses it proffers is responsible for making all necessary arrangements and paying all costs and expenses associated with the use of an interpreter.
39 C.F.R. §955.21