Summary: If you want to request a payment from someone then writing a letter is good way. A letter for requesting payment must be written in such a way that it will still have the tact needed to maintain professionalism. A few considerations must be done in order to make your request granted promptly. If you are writing this kind of letter, here is a sample for you.
July 12, 2010
Mr. Anthony Brown,
This letter serves as my notice that I am asking for the payments for the accounts for March 2010, having a credit of $3000. I have constantly waited for this sum of money for a couple of days and it has affected my work. Feel free to check the invoice (no.567) that is attached herewith and we have not had any payment received for this. Please pay the said amount in a month time and it will surely be a big help,if not an interest will be charged at 5% in each month.
Discard this letter if payment is already made. I am positve for doing more business with you. Waiting for your reply.
Mr. John Stone