This goes beyond conscription into the realm of outright ~Slavery~.
No, compelling someone to do something does not count as slavery.
There are plenty of reasons why Apple should refuse to comply with the court order but preventing slavery isn't one.
There is a case to be had as to whether Apple is obstructing the course of justice or even acting as accessory – I personally don't think it is – and the courts will have to decide. There is also the idea that the FBI doesn't really care about this phone – it already has access to the backups and the metadata –but wants a precedent decision so that hardware encryption, for which no backdoor cannot be created post-hoc, can be declared illegal.
Let's hope the US Supreme Court is complete by the time this case eventually makes it there.
Biting the hand that feeds IT
