Dear

As a good businessman, you are aware of the manner in which
accounts that have become seriously past due must be handled.
I am not going to attempt to think of some clever phrase or
witty jingle to get your attention.  Neither do I wish to
embarrass, intimidate or do any of the nasty things that are
often done to encourage payment.

I am merely informing you that the account has reached a
point where we must decide within a few days whether to turn
it over for collection or just hand it to our attorneys,
neither of which is our preference.

We know that you understand our predicament and are probably
experiencing a similar situation with some of your aging
accounts.

We would like to hear from you and learn what your intentions
are in regard to this account.