(Reuters) - Digital privacy advocates have called on a U.S. federal judge to approve Apple Inc's (>> Apple Inc.) request not to be compelled to build software to help the FBI unlock an iPhone used by one of the shooters in the San Bernardino attack.

The American Civil Liberties Union, Access Now and the Wickr Foundation laid out arguments in amicus briefs released on Wednesday ahead of a March 22 hearing in which Judge Sheri Pym will review Apple's appeal of a court order demanding it help unlock a phone used by Rizwan Farook.

Alphabet Inc's (>> Alphabet Inc) Google, Facebook Inc (>> Facebook Inc), Microsoft Corp (>> Microsoft Corporation) and Twitter Inc (>> Twitter Inc) also plan to file similar briefs, Twitter, Microsoft and people familiar with the plans of the other two companies said last week. [L2N1642BW]

The ACLU argued that the FBI's request would undermine the privacy and security of Americans by forcing a private firm to act as its investigative agent, seeking information that it does not already possess.

"Law enforcement may not commandeer innocent third parties into becoming its undercover agents, its spies, or its hackers," according to a draft of the brief obtained by Reuters.

Access Now and the Wickr Foundation, which both advise activists on digital privacy, said in a joint brief that complying with the order would undermine human rights around the globe.

"In some countries reliable security tools such as encryption can be the difference between life and death," their brief says. "The relief sought by the government endangers people globally who depend on robust digital security for their physical safety and wellbeing."

The U.S. government has said the Dec. 2 attack in San Bernardino, California, was inspired by Islamist militants, and the FBI wants to read the data on Farook's phone to investigate any links with militant groups. Farook and his wife, Tashfeen Malik, shot and killed 14 people and wounded 22 others before they themselves were killed in a shootout with police.

(Reporting by Jim Finkle; Editing by Paul Simao)