Wainstein didn't immediately respond to a request for a comment on the memo he authored. The DOJ memo came in response to an NSA request seeking to clarify that it had authorization to collect Internet metadata from U.S. residents.
NSA critics have said that the collection of metadata, including the recipients of phone calls and email and the time of the calls and emails, can tell a great deal about a person and is a privacy violation.
The NSA U.S. collections are "pretty outrageous," digital rights activist Sina Khanifar said in an email. "Anyone who claims that the NSA's surveillance hasn't been in violation of our Fourth Amendment rights is going to have a much harder time making that argument in light of this news."
Khanifar helped launch the website StopWatching.us two weeks ago, and the site has collected more than 512,000 signatures of people calling on the U.S. government to stop spying on them.
Sign up for CIO Asia eNewsletters.