The Electronic Frontier Foundation has been successful in having a secret document released by the U.S. government, that helps U.S. authorities to interpret the federal snooping law, the Foreign Intelligence Services Act (FISA).
The trouble is, the document is pretty much entirely all redacted. (So much for transparency...)
In a nutshell, last month the U.S. Congress reauthorized the FISA Amendments Act for another five years, allowing the U.S. government and its law enforcement agencies to conduct "unconstitutional surveillance," according to the EFF. However, the law is complicated and lengthy, and there is a "secret interpretation" of the law that allows U.S. authorities to know whether they can conduct wiretapping and snooping on U.S. citizens and non-residents.
Source: CNet. Read full article. (link)