Google, Amazon, Facebook, and Microsoft, along with other technology companies, filed numerous court briefs attacking the U.S. government’s legal arguments against Apple in the privacy and data security case involving the iPhone used by a gunman in a terrorist attack in San Bernardino, Calif., last year.

Support for Apple from other tech companies, including many rivals, underscores how high the stakes are for the industry with the case, testing the limits of government access to personal data. Federal authorities are demanding Apple’s help to break into the iPhone.

Edward J. McAndrew, a lawyer at Ballard Spahr who is not involved in the Apple matter, said it was highly unusual to see a flood of briefs by so many parties this early in a case. He called the outpouring “Supreme Court-level advocacy” and said the campaign was intended to have influence beyond the court with legislators and others.

“This is a show of force,” said Mr. McAndrew, a former federal prosecutor who focused on online crimes. “This is a battle for public opinion.”

Related Practice