Google Inc., Microsoft Corp. and other tech giants asked for permission to join Facebook Inc.’s legal fight against an Israeli company that the social media company accuses of installing malware on the phones of unsuspecting users.

The companies asked the federal appeals court in San Francisco on December 21 to let them file a motion in support of a lawsuit that WhatsApp, Facebook’s messaging service, brought last year against NSO Group.

WhatsApp accused the spyware maker of using a since-closed vulnerability in the messaging service to install spyware on the phones of at least 1,400 users. The spyware allowed NSO to surreptitiously collect data from users’ phones, according to the suit.

Allowing companies like NSO to deploy cyber-surveillance tools across U.S. systems creates large-scale, systemic cybersecurity risk, the tech companies said in the brief at the appeals court.

NSO says it can’t be sued in a U.S. court because it was doing its work as an agent of foreign governments and so is entitled to foreign sovereign immunity. U.S. District Judge Phyllis Hamilton in Oakland, California, in July denied NSO’s request to dismiss the lawsuit.

The tech companies urged the appeals court to treat NSO like any other company doing business in the U.S. In their brief, the companies described NSO’s cyber-surveillance tools as “dangerous” and said they could be “exploited by malicious actors other than the initial customer to cripple infrastructure, commit large-scale financial crime, or cause other catastrophic damage.”

Google and Microsoft were joined in their request by Cisco Systems Inc., GitHub, Inc., LinkedIn Corp., VMware Inc., and the lobbying group, the Internet Association.

Reuters reported on the filing earlier.