Rights groups Amnesty International and Human Rights Watch (HRW) responded immediately, saying that if the allegation was true, it could prove harmful to their employees, contacts and work.

“This raises the very real possibility that our communications with confidential sources have been intercepted,” Michael Bochenek, senior director of International Law and Policy at Amnesty International, said Tuesday in a statement. “Sharing this information with other governments could put human rights defenders the world over in imminent danger.”

In a separate statement, HRW General Counsel Dinah Pokempner said that the revelation was "indicative of the overreach that U.S. law allows to security agencies."

Also on Tuesday, the European Union’s highest court overturned a law forcing telecommunication operators to store users’ private telephone and email data for up to two years — a practice the NSA has been widely criticized for.

The European Court of Justice said that the 2006 Data Retention Directive “interferes in a particularly serious manner with the fundamental rights to respect for private life and to the protection of personal data.”

The law was enacted in the wake of deadly attacks in Europe, including the 2004 train bombings in Madrid and the 2005 bombings in London. The decision to overturn the law comes as Europeans continue to weigh concerns over electronic snooping, brought to the public’s attention by Snowden’s NSA revelations.

Snowden had previously revealed that the U.S. agency collected data on millions of European citizens and eavesdropped on German Chancellor Angela Merkel’s mobile phone — sparking a wave of controversy that prompted lawmakers on both sides of the Atlantic to rethink their data surveillance laws.

Al Jazeera and wire services