WASHINGTON (Reuters) -- Apple Inc opposed a court ruling on Tuesday that ordered it to help the FBI break into an iPhone recovered from a San Bernardino shooter, heightening a dispute between tech companies and law enforcement over the limits of encryption.
Chief Executive Tim Cook said the court's demand threatened the security of Apple's customers and had "implications far beyond the legal case at hand."
Earlier on Tuesday, Judge Sheri Pym of U.S. District Court in Los Angeles said that Apple must provide "reasonable technical assistance" to investigators seeking to unlock the data on an iPhone 5C that had been owned by Syed Rizwan Farook.
That assistance includes disabling the phone's auto-erase function, which activates after 10 consecutive unsuccessful passcode attempts, and helping investigators to submit passcode guesses electronically.
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Apple opposes order to help unlock Calif. shooter's phone
SAN FRANCISCO, CA - MARCH 9: Apple CEO Tim Cook gestures on stage during an Apple special event at the Yerba Buena Center for the Arts on March 9, 2015 in San Francisco, California. Apple Inc. announced the new MacBook as well as more details on the much anticipated Apple Watch, the tech giant's entry into the rapidly growing wearable technology segment as well (Photo by Stephen Lam/Getty Images)
Apple interim CEO and Chief Operating Officer Tim Cook smiles before the start of the the Apple Worldwide Developers Conference in San Francisco, Monday, June 8, 2009. Cook is the interim CEO while Steve Jobs is out on leave. (AP Photo/Paul Sakuma)
In this July 16, 2010 photo shows Apple's Tim Cook, left, and Steve Jobs, right, during a meeting at Apple in Cupertino, Calif. Cook takes over as CEO for Apple after Jobs resigned. (AP Photo/Paul Sakuma)
Apple CEO Tim Cook during announcement at Apple headquarters in Cupertino, Calif., Tuesday, Oct. 4, 2011. (AP Photo/Paul Sakuma)
SAN FRANCISCO, CA - MARCH 9: Apple CEO Tim Cook stands in front of an MacBook on display after an Apple special event at the Yerba Buena Center for the Arts on March 9, 2015 in San Francisco, California. Apple Inc. announced the new MacBook as well as more details on the much anticipated Apple Watch, the tech giant's entry into the rapidly growing wearable technology segment as well (Photo by Stephen Lam/Getty Images)
Apple CEO Tim Cook smiles before speaking to graduates during George Washington University's commencement exercises on the National Mall, Sunday, May 17, 2015 in Washington. The university awarded Cook with an honorary doctorate of public service. (AP Photo/Alex Brandon)
SAN FRANCISCO, CA - MARCH 9: Apple CEO Tim Cook waves from stage after an Apple special event at the Yerba Buena Center for the Arts on March 9, 2015 in San Francisco, California. Apple Inc. announced the new MacBook as well as more details on the much anticipated Apple Watch, the tech giant's entry into the rapidly growing wearable technology segment as well (Photo by Stephen Lam/Getty Images)
Apple CEO Tim Cook responds to a question during a news conference at IBM Watson headquarters, in New York, Thursday, April 30, 2015. Apple, IBM and Japanese insurance and bank holding company Japan Post have formed a partnership to improve the lives of elderly people in the country. The program will provide iPads with apps designed to help seniors manage day-to-day lives and keep in touch with family members. (AP Photo/Richard Drew)
Apple chief executive and Alabama native Tim Cook, right, and Catherine Randall pose with a plaque during an Alabama Academy of Honor ceremony at the state Capitol Monday, Oct. 27, 2014, in Montgomery, Ala. Cook and seven others, including Alabama football head coach Nick Saban, were inducted into the Alabama Academy of Honor. (AP Photo/Brynn Anderson)
Apple CEO Tim Cook introduces the new Apple iPad Air 2 during an event at Apple headquarters on Thursday, Oct. 16, 2014 in Cupertino, Calif. (AP Photo/Marcio Jose Sanchez)
Tim Cook, CEO of Apple Inc., smiles as he visits the Apple Store during the launch and sale of the new iPhone 6 on Friday, Sept 19, 2014 Palo Alto, Calif. (AP Photo/Tony Avelar)
Tim Cook, CEO of Apple Inc takes a photograph with Apple employees at the Apple Store during the launch and sale of the new iPhone 6 on Friday, Sept 19, 2014 Palo Alto, Calif. (AP Photo/Tony Avelar)
Apple CEO Tim Cook discusses the new Apple Watch and iPhone 6 on Tuesday, Sept. 9, 2014, in Cupertino, Calif. (AP Photo/Marcio Jose Sanchez)
Apple's CEO Tim Cook gestures during a promotional event that marks the opening day of sales of China Mobile's 4G iPhone 5s and iPhone 5c at a shop of the world's largest mobile phone operator in Beijing, China, Friday, Jan. 17, 2014. (AP Photo/Alexander F. Yuan)
Apple CEO Tim Cook speaks during an event to announce new products in San Jose, Calif., Tuesday, Oct. 23, 2012. (AP Photo/Marcio Jose Sanchez)
FILE- In this Wednesday, March 7, 2012, file photo, Apple CEO Tim Cook announces a new iPad during an Apple announcement in San Francisco. Apple CEO Tim Cook is expected to show off new iPhone software, updated Mac computers and provide more details on future releases of Mac software when he kicks off the company's annual conference for software developers on Monday, June 11, 2012. (AP Photo/Paul Sakuma)
FILE - In a Wednesday, March 7, 2012 file photo, Apple CEO Tim Cook announces a new iPad during an Apple announcement in San Francisco. On Tuesday, April 10, 2012, Apple, already the world's most valuable company, hit the $600 billion level for the first time. (AP Photo/Paul Sakuma, File)
Tim Cook, chief executive officer of Apple Inc., right, waves to customers while leaving the sales launch for the iPhone 6 and iPhone 6 Plus at the Apple Inc. store in Palo Alto, California, U.S., on Friday, Sept. 19, 2014. Apple Inc.'s stores attracted long lines of shoppers for the debut of the latest iPhones, indicating healthy demand for the bigger-screen smartphones. The larger iPhone 6 Plus is already selling out at some stores across the U.S. Photographer: David Paul Morris/Bloomberg via Getty Images
Tim Cook, chief executive officer of Apple Inc., left, and the band U2 gesture during a product announcement at Flint Center in Cupertino, California, U.S., on Tuesday, Sept. 9, 2014. Apple Inc. unveiled redesigned iPhones with bigger screens, overhauling its top-selling product in an event that gives the clearest sign yet of the company's product direction under Cook. Photographer: David Paul Morris/Bloomberg via Getty Images
CUPERTINO, CA - OCTOBER 16: Apple CEO Tim Cook speaks during an Apple special event on October 16, 2014 in Cupertino, California. Apple unveiled the new iPad Air 2 tablet, iPad Mini 3 and a Retina iMac. (Photo by Justin Sullivan/Getty Images)
SAN FRANCISCO, CA - JUNE 02: Apple CEO Tim Cook walks off stage after speaking during the Apple Worldwide Developers Conference at the Moscone West center on June 2, 2014 in San Francisco, California. Tim Cook kicked off the annual WWDC which is typically a showcase for upcoming updates to Apple hardware and software. The conference runs through June 6. (Photo by Justin Sullivan/Getty Images)
BEIJING, CHINA - JANUARY 17: (CHINA OUT) Tim Cook, Chief Executive Officer of Apple Inc., visits a China Mobile shop to celebrate the launch of iPhone 5S and iPhone 5C on China Mobile's fourth generation (4G) network on January 17, 2014 in Beijing, China. Apple Inc. and China Mobile Limited, the world's largest carrier with over 760 million subscribers, signed a deal on December 23, 2013 after six years of negotiations. (Photo by ChinaFotoPress/ChinaFotoPress via Getty Images)
Tim Cook, chief executive officer of Apple Inc., displays the iPad Air for a photograph during a press event at the Yerba Buena Center in San Francisco, California, U.S., on Tuesday, Oct. 22, 2013. Apple Inc. introduced new iPads in time for holiday shoppers, as it battles to stay ahead of rivals in the increasingly crowded market for tablet computers. Photographer: Noah Berger/Bloomberg via Getty Images
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Federal prosecutors requested the court order to compel Apple to assist the investigation into the Dec. 2 shooting rampage by Farook and his wife, killing 14 and injuring 22 others. The two were killed in a shootout with police.
The FBI has been investigating the couple's potential communications with Islamic State and other militant groups.
"Apple has the exclusive technical means which would assist the government in completing its search, but has declined to provide that assistance voluntarily," prosecutors said.
U.S. government officials have warned that the expanded use of strong encryption is hindering national security and criminal investigations.
Technology experts and privacy advocates counter that forcing U.S. companies to weaken their encryption would make private data vulnerable to hackers, undermine the security of the Internet and give a competitive advantage to companies in other countries.
In a letter to customers posted on Apple's website, Cook said the FBI wanted the company "to build a backdoor to the iPhone" by making a new version of the iPhone operating system that would circumvent several security features.
"The government is asking Apple to hack our own users and undermine decades of security advancements that protect our customers -- including tens of millions of American citizens -- from sophisticated hackers and cybercriminals." -- Tim Cook, Apple CEO
He said Apple was "challenging the FBI's demands" and that it would be "in the best interest of everyone to step back and consider the implications."
In a similar case last year, Apple told a federal judge in New York that it was "impossible" for the company to unlock its devices that run an operating system of iOS 8 or higher.
According to prosecutors, the phone belonging to Farook ran on iOS 9.
Prosecutors said Apple could still help investigators by disabling "non-encrypted barriers that Apple has coded into its operating system."
Apple and Google both adopted strong default encryption in late 2014, amid growing digital privacy concerns spurred in part by the leaks from former National Security Agency contractor Edward Snowden.
Forensics expert Jonathan Zdziarski said on Tuesday that Apple might have to write custom code to comply with the order, presenting a novel question to the court about whether the government could order a private company to hack its own device.
Zdziarski said that, because the San Bernardino shooting was being investigated as a terrorism case, investigators would be able to work with the NSA and the CIA on cracking the phone.
Those U.S. intelligence agencies could likely break the iPhone's encryption without Apple's involvement, he said.