29 U.S. Code § 1862 - Authority to obtain information
To carry out this chapter the Secretary, either pursuant to a complaint or otherwise, shall, as may be appropriate, investigate, and in connection therewith, enter and inspect such places (including housing and vehicles) and such records (and make transcriptions thereof), question such persons and gather such information to determine compliance with this chapter, or regulations prescribed under this chapter.
The Secretary may issue subpenas requiring the attendance and testimony of witnesses or the production of any evidence in connection with such investigations. The Secretary may administer oaths, examine witnesses, and receive evidence. For the purpose of any hearing or investigation provided for in this chapter, the authority contained in sections 49 and 50 of title 15, relating to the attendance of witnesses and the production of books, papers, and documents, shall be available to the Secretary. The Secretary shall conduct investigations in a manner which protects the confidentiality of any complainant or other party who provides information to the Secretary in good faith.
It shall be a violation of this chapter for any person to unlawfully resist, oppose, impede, intimidate, or interfere with any official of the Department of Labor assigned to perform an investigation, inspection, or law enforcement function pursuant to this chapter during the performance of such duties.