I don't think this could happen without enabling legislation.
The U.S. military draft required passage of the Selective Service Act [1] Something similar would be required before Apple's coders could be forced to carry out court orders directed at Apple, the corporation. Even in these times (so far!) I think this wouldn't happen.
Unfortunately I'm sure there are at least a few engineers with the expertise necessary who would happily agree to work with the FBI (for whatever reason.)
I think it's become clear that they'd at least try.