Section 7 of PL 93-579
[the Federal
Privacy Act of 1974, 5 USC 552a note]
Sec. 7 (a)(1) It shall be unlawful for any Federal, State or local government
agency to deny to any individual any right, benefit, or privilege provided by
law because of such individual's refusal to disclose his social security
account number.
(2) the provisions of paragraph (1) of this subsection shall not apply with
respect to--
(A) any disclosure which is required by Federal statute, or
(B) any disclosure of a social security number to any Federal, State, or local
agency maintaining a system of records in existence and operating before
January 1, 1975, if such disclosure was required under statute or regulation
adopted prior to such date to verify the identity of an individual.
(b) Any Federal, State or local government agency which requests an individual
to disclose his social security account number shall inform that individual
whether that disclosure is mandatory or voluntary, by what statutory or other
authority such number is solicited, and what uses will be made of it.
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See also a somewhat dated