Make the letter exactly that - a friendly reminder! This is not yet the time for threats - leave that for the lawyers at the right time. At this stage a note like: `This is just a friendly reminder to inform you that your account was due for payment on .... We always like to maintain the close relationship that we have with our clients, and would want the same thing between ourselves. Please do your best to make payment before ...` etc.
Read more: Help create introduction speech for collecting outstanding payments from customers/ clients? - Help create introduction speech for collecting outstanding payments from customers/ clients :: Ask Me Fast at http://www.askmefast.com/Help_create_introduction_speech_for_collecting_outstanding_payments_from_customers_clients-qna6572588.html