How likely is it for a person on probation to have it revoked for being behind on restitution?

Question Details:

I am halfway through a 5 year probation sentence (I never served prison time) for "providing false information on a federal document." I am several months behind on restitution payments (which have already been lowered). I was sent a letter saying my probation may be revoked for "willfully refusing to pay" my restitution. I have simply been unable to pay. I know they may garnish my wages if I am not sent to prison, but that doesn't make sense either. It will be 25% of what I make. If the court recognized I couldn't make the payments before, how is it reasonable to take so much from my check? Important Notice