39 CFR 965.9: Evidence.

(a) In general, admissibility will hinge on relevancy and materiality. However, relevant evidence may be excluded if its probative value is substantially outweighed by the danger of unfair prejudice, or by considerations of undue delay, waste of time, or needless presentation of cumulative evidence.

(b) Testimony shall be given under oath or affirmation and witnesses are subject to cross-examination.