Critics have accused Chancellor Angela Merkel's staff of giving the nod to the BND to help the NSA spy on European firms and officials. They also say officials lied about the prospects of a U.S.-German "no-spy deal" before the 2013 election.

Polls show the scandal is starting to hurt popular Merkel whose office is responsible for the oversight of intelligence. 

Citing confidential documents, Die Zeit Online reported on Tuesday that of about 220 million pieces of meta data gathered per day, some 1.3 billion pieces per month go to the NSA.

The data includes raw material from phone calls and text messages which shows contact details and times of activity but does not contain content. In particular, it sends raw material on foreign communication in crisis regions, said Zeit Online.

"It is questionable as to whether this practice is covered by German laws," wrote Die Zeit, citing a BND official responsible for data protection.