Secrecy News, the invaluable newsletter put out by the Federation of American Scientists, has obtained an August 2004 Department of Homeland Security memo [PDF] that it describes as "a massive increase in government secrecy."
In a momentous expansion of the apparatus of government secrecy, the [DHS] is requiring employees and others to sign legally binding non-disclosure agreements as a condition of access to certain categories of unclassified information.
Up to now, non-disclosure agreements have only been used by government agencies to regulate access to classified information. In fact, they are one of the defining features of the national security classification system, along with security clearances and the "need to know" principle. As far as Secrecy News could determine, such classification-like controls have never before been systematically imposed on access to unclassified information.
This decision, up until now, has been secret.