36 C.F.R. § 1202.22

(a) Before a NARA employee or NARA contractor asks you to provide your social security number (SSN), he or she will ensure that the disclosure is required by Federal law or under a Federal law or regulation adopted before January 1, 1975.

(b) If you are asked to provide your SSN, the NARA employee or contractor must first inform you:

(1) Whether the disclosure is mandatory or voluntary;

(2) The statute or authority under which your SSN is solicited; and

(3) How your SSN will be used.