29 CFR §458.51

In connection with such investigation the Chief, DOE or a District Director or his representative may inspect such records and question such persons as he may deem necessary to enable him to determine the relevant facts. Every labor organization, its officers, employees, agents, or representatives shall cooperate fully in any investigation and shall testify and produce the records or other documents requested in connection with the investigation. This section shall be enforced in accordance with the procedures in §§ 458.66 through 458.92.