According to the new law, German intelligence is subject to more federal government oversight, but at the same time it authorizes the BND to target foreign nationals as well as EU institutions and member states.
Apart from this, the BND will still be allowed to work with the US National Security Agency (NSA), but only under certain strict conditions: to fight terrorism or to protect Germany's national security.
The adoption of the legislation followed the revelations that the BND had secretly colluded with the NSA in snooping on European politicians and companies.
"Those German lawmakers who represent the country's ruling coalition know that they have adopted an unconstitutional law," Herrmann said, adding that the document contains no provisions to protect journalists, lawyers or doctors from Germany and beyond.
He slammed the government for its reluctance to hold an open discussion about "how law should respect human rights and what is necessary and what is not."
"But they just adopted the law, which runs counter to German constitution, with the court now authorized to decide which is right and which is not," he added.
Herrmann also said that "freedom of press is really endangered with this law," and that public organizations in Germany are expected to file a relevant lawsuit.
Although the majority of German MPs voted in favor of the legislation, it drew sharp criticism from the country's Left party and the Green party, which claim that the new law has simply legalized spying on the population.
"But let me remind you that in certain cases — when the legislation was violated — the federal government worked together with intelligence," he said.
Last April, an espionage scandal gripped Germany as local media uncovered that the BND had provided technical assistance to the NSA in spying on European targets, including top political figures and corporations.The BND is believed to have spied on some 800,000 IP addresses, phone numbers and email addresses at the request of US intelligence.
