"The BND systematically lifted and used personal data without a legal basis to do so," wrote the commissioner.
Voßhoff named a total of 12 violations of the law in seven spheres of activity, including obstruction of her own work.
"The BND massively and illegally blocked my ability to oversee it — a comprehensive and efficient oversight on my part was therefore not possible. These are serious breaches of the law."
According to the report, the commissioner was blocked from checking so-called selectors — the lists of the key concepts, which identify information such as phone numbers and email addresses used by the BND for targeted surveillance.
Opposition politicians said that the report confirmed what they had long been saying — that the BND acts outside the law.
"The report cannot be misunderstood, either in its unusual level of clarity or in the extent of its criticism," said Konstantin von Notz, Green Party Member of Parliament and head of the parliamentary committee on the NSA.
Activities of the Germany's Federal Intelligence Service attracted the attention of the German public and the Bundestag after the scandalous revelations of Edward Snowden. BND management was accused of helping the American NSA, when it was spying on a global scale. It was revealed that the NSA tapped a number of European governments and organizations, including German ones.