Read this http://www.parentnook.com/forum/viewtopic.php?f=161&t=3934 it will answer your question. Others (here) might ell you to ignore letter that is a choice yo alone must make but again post I supplied so you are at least aware of what "could" happen if you fail to pay
You have no obligation whatsoever to pay the fee. You don't have to pay anything at all unless ordered to by a court.
Whether you SHOULD pay the fee depends on various factors. I suggest you take the letter to a local attorney for some quick advice on how these matters are typically handled in your area.