Leading tech giants including Microsoft and Google on Monday, December 21, joined Facebook’s legal battle against Israeli surveillance firm, NSO Group, accusing it of allegedly using powerful and dangerous tools.

The two companies filed an amicus brief before the U.S Court of Appeals opens up a new front in Facebook’s lawsuit against the Israeli spyware firm, according to Reuters.

Facebook sued NSO Group last year after it emerged that the cyber-surveillance firm had exploited a bug in Facebook-owned platform WhatsApp to help track more than 1,400 people worldwide.

However, the tech firm denied the allegations, arguing that because it sells digital break-in tools to police and spy agencies, it should benefit from sovereign immunity.

At the time, Dell technologies-owned VMW and the Washington-based internet Association joined forces with Facebook to contradict that, citing that awarding sovereign immunity to NSO would lead to the proliferation of hacking technology and that "more foreign governments with powerful and dangerous cyber-surveillance tools.”

Reports indicate that NSO lost that argument and has since appealed to the Ninth Circuit in order to have the ruling overturned.

Sovereign immunity is basically a legal doctrine whereby a sovereign state cannot commit a legal wrong and is immune to civil suit or criminal prosecution.

Meanwhile, the tech firm has put a new human rights policy in place to prevent and mitigate abuse of its spyware.

The policy, among others, states that NSO Group customers have contractual obligations to limit the use of the company’s products to the prevention and investigation of serious crimes, including terrorism, and to also ensure that the products will not be used to violate human rights.