Treas. Reg. § 1.501(c)(9)-5

(a) Records. In addition to such other records which may be required (for example, by section 512(a)(3) and the regulations thereunder), every organization described in section 501(c)(9) must maintain records indicating the amount contributed by each member and contributing employer, and the amount and type of benefits paid by the organization to or on behalf of each member.

(b) Cross reference. For provisions relating to annual information returns with respect to payments, see section 6041 and the regulations thereunder.