"You must do X to keep your job," where X in this case is something onerous but still doable for most (like moving to a different city so you can work in-office

"You must do X to keep your job," where X in this case is something onerous but still doable for most (like moving to a different city so you can work in-office). If you refuse to do the onerous thing, then you're voluntarily refusing to do that which keeps your job. Therefore, it's a voluntary resignation.