.. 1789 law, the All Writs Act, says that the government can order someone to do anything necessary to comply to an existing writ, so long as the government’s request is not “unduly burdensome.”
.. So the FBI is using the All Writs Act to say that Apple must engineer a new version of its operating platform in order to comply with the warrant.
Apple is saying that such a request violates the “unduly burdensome” caveat. And that’s where the issue stands today.