The FBI is currently relying on the All Writs Act of 1789 to compel Apple into action, though the tech giant has refused (or at least is unable) to build a backdoor into its operating system for the federal law enforcement agency. Apple CEO Tim Cook has vowed to fight the order all the way to the Supreme Court and has classified the directive as "chilling" and "dangerous". The FBI, for its part, claims that it is "not trying to set a precedent" -- even though that is precisely what it will do.

Microsoft is also battling the US government over a similar situation. The government has ordered Microsoft to hand over a suspected drug trafficker's emails, which reside on one of the company's servers. Apple has thrown its support behind Microsoft in that case, which is awaiting a ruling by an appellate court judge.