I am not an HR guru either, but it's my understanding that a employer can require you to use your accrued leave prior to placing you on unpaid FMLA leave. You also have to be reinstated with the full benefit package that you had prior to the leave taking place. While I reviewed the statute, I did not see it addressing unaccrued leave, but in my reading, I would have to say they are skating on thin ice by requiring you to use unaccrued leave. I don't think that is in the spirit of the law. I would make a call to a local employement attorney for a definitive answer.
The opinions expressed are my own, take them or leave them.