SAMPLE - WILL REMIT WHEN WORK IS COMPLETE

[NAME, COMPANY AND ADDRESS]

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

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,