Apple argues granting that access might mean the US government, other countries or sophisticated cyber criminals could use the approach again.
But the government argues the phone offers crucial evidence in investigating one of the country's worst attacks involving people lured by the self-proclaimed Islamic State, or IS.
It has reignited debate about national security versus privacy concerns.
Syed Farook and his wife Tashfeen Malik killed 14 people in San Bernadino, California, last December before police shot them dead.
The FBI has since been looking into any possible links between Farook and IS.
As part of that investigation, the FBI wants to be able to access Farook's iPhone.
It wants to be able to try different combinations in rapid sequence until it finds the right one.
Currently, Apple's encryption software means the iPhone erases all of its data after 10 consecutive failed password attempts.
Encryption is a process of encoding messages or information so they can only be accessed by authorised parties and, for example, criminals or governments cannot intercept them.
Because of such software, not even Apple itself can access personal data on a phone.
But a US Magistrate Court judge has ordered Apple to help the FBI break into the iPhone.
In a statement posted on its website, Apple's chief executive Tim Cook says unlocking it would set a dangerous precedent.
"The United States government has demanded that Apple take an unprecedented step which threatens the security of our customers. We oppose this order, which has implications far beyond the legal case at hand. Some would argue that building a backdoor for just one iPhone is a simple, clean-cut solution. The government suggests this tool could only be used once, on one phone. But that's simply not true. Once created, the technique could be used over and over again, on any number of devices.The implications of the government's demands are chilling. If the government can use the All Writs Act to make it easier to unlock your iPhone, it would have the power to reach into anyone's device to capture their data. The government could extend this breach of privacy and demand that Apple build surveillance software to intercept your messages, access your health records or financial data, track your location, or even access your phone's microphone or camera without your knowledge."
Former CIA agent Patrick Skinner agrees.
He argues recent incidents, such as last year's hacking of the US Office of Personnel Management, highlight the concerns around potential security breaches.
"Having a lot of experience with the government, it's not that they're ill-intended, but there's a lot of competency issues. I'm not afraid that the government's going to go against me. Now that is a legitimate concern for a lot of people elsewhere, but my concern is more about the actual security of the information. It's not a single-case issue. You don't pick exceptions and build precedents. So by weakening something, if they create it, they will use it elsewhere. And it's not just that. If you give the US government keys, they're going to lose it. I've already had to change my credit protection twice this year because of the OPM hack. In a land of locks, if you give somebody the master key, they become king, and I don't think that the US government should have that right now."
But White House spokesman Josh Earnest maintains the FBI is simply asking for access to one device.
"They are not asking Apple to redesign its product or to create a new backdoor to one of their products. They're simply asking for something that would have an impact on this one device."
Tim Stevens, from the technology website C-Net, has told Al Jazeera that Apple is not the only company preventing governments from accessing consumer information.
"This is definitely something that is across the industry at this point. Both Apple and Google have instituted encryption technologies within their mobile operating systems to prevent themselves from being able to decrypt these devices. So it's the same on an android device as it is on an iPhone. So this is a pretty common case in the industry, and, again, the government's trying to get some sort of backdoor, some kind of skeleton key, added to these encryption technologies to allow these devices to be decrypted."
Apple says it will contest the ruling.
Share
