Apple is vowing to fight a court's order issued last week telling them to help feds build a "backdoor" to the iPhone belonging to one of the shooters in the San Bernardino terrorist attack.

In a letter posted on the company's website on Tuesday evening, Apple CEO Tim Cook wrote, "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."

According to Cook, Apple does not currently have the software that the FBI wants in order to access the data on a work phone that belonged to Syed Farook, one of the attackers in the shooting. "The FBI wants us to make a new version of the iPhone operating system, circumventing several important security features, and install it on an iPhone recovered during the investigation," explains Cook. "In the wrong hands, this software—which does not exist today—would have the potential to unlock any iPhone in someone's physical possession."

"Building a version of iOS that bypasses security in this way would undeniably create a backdoor," he continues. "And while the government may argue that its use would be limited to this case, there is no way to guarantee such control."

Cook says that creating the backdoor for the FBI would essentially be Apple being asked to "hack our own users" and undermine the security the company has created for their customers. "The same engineers who built strong encryption into the iPhone to protect our users would, ironically, be ordered to weaken those protections and make our users less safe," he writes.

In the same letter, Cook also calls out the federal government's invoking of the All Writs Act, saying it establishes "a dangerous precedent." "If the government can use the All Writs Act to make it easier to unlock your iPhone," Cook says, "it would have the power to reach into anyone's device to capture their data."

"Opposing this order is not something we take lightly. We feel we must speak up in the face of what we see as an overreach by the U.S. government."

Apple has yet to take any further steps in this case, but an appeal is likely. The tech giant already has the backing of the Electronic Frontier Foundation, who issued a statement yesterday pledging their support. "We are supporting Apple here because the government is doing more than simply asking for Apple's assistance," writes EFF Deputy executive director Kurt Opsahl. "For the first time, the government is requesting Apple write brand new code that eliminates key features of iPhone security—security features that protect us all."

According to the L.A. Times the last time Farook's iPhone sent backup data to an iCloud server was on October 19, about a month and a half before the attack in San Bernardino. Any data after that date would only be accessible from the phone itself.

Farook and his wife Tashfeen Malik opened fire at a work banquet on December 2, killing 14 people. They were later killed in a shootout with police. The FBI is investigating the attack as an act of terrorism.