29 U.S. Code § 2616 - Investigative authority
(a) In general
(b) Obligation to keep and preserve records
(c) Required submissions generally limited to annual basis
The Secretary shall not under the authority of this section require any employer or any plan, fund, or program to submit to the Secretary any books or records more than once during any 12-month period, unless the Secretary has reasonable cause to believe there may exist a violation of this subchapter or any regulation or order issued pursuant to this subchapter, or is investigating a charge pursuant to section 2617 (b) of this title.
(d) Subpoena powers
For the purposes of any investigation provided for in this section, the Secretary shall have the subpoena authority provided for under section 209 of this title.