"…prohibits you…from disclosing this letter, other than to…an attorney to obtain legal advice or legal assistance with respect to this letter.""
Source: http://upload.wikimedia.org/wikipedia/commons/9/91/EFF-IA_Na...
I can't see a reasonable way of establishing bona fides other than creating a strong implication/inference of "national security".
(My wife is a federal attorney, and it is disappointing how warped "the government's" perspectives are on rights and what is reasonable.)