Earlier this year, Snowden gave documents to the Post and Britain's Guardian newspaper disclosing U.S. surveillance programs that collect vast amounts of phone records and online data in the name of foreign intelligence, often sweeping up information on American citizens.
The collection of contact lists in bulk would be illegal if done in the United States, but the Post said the agency can get around that restriction by intercepting lists from access points around the world.
The newspaper quoted a senior intelligence official as saying NSA analysts may not search or distribute information from the contacts database unless they can "make the case that something in there is a valid foreign intelligence target in and of itself."
Commenting on the Post story, Alex Abdo, a staff attorney with the American Civil Liberties Union, said in an emailed statement: "This revelation further confirms that the NSA has relied on the pretense of 'foreign intelligence gathering' to sweep up an extraordinary amount of information about everyday Americans. The NSA's indiscriminate collection of information about innocent people can't be justified on security grounds, and it presents a serious threat to civil liberties."