[DATE, ex. Monday, March 31, 2008]

[NAME, COMPANY AND ADDRESS, ex.
Link Building
XYZ Inc.
1234 First Street
Suite 567
Anycity, Anystate  85245]

Dear [NAME, ex. Link Building],

I am in receipt of your invoice #[INVOICE NUMBER], dated [DATE, ex. June 8, 1998].

Since [STATE WHAT STILL NEEDS TO BE DONE, ex. Units 5, 6 and 12 of our construction site still require clean up and disposal], I am unable to pay you at the moment.  I will be pleased, however, to send you a check in the amount of $[AMOUNT] once the above work which we agreed upon is completed. 

Sincerely,

[YOUR NAME, ex. Jill Jones]