Dear :

We are very concerned about the delay in our order for [product] (Order No. ). When we placed this order with you on [date], we were assured that we would receive the [product] by [date] at the latest.

I would like to remind you that this was the third time that our orders were delayed. These delays have caused us to miss deadlines with our customers and placed us in a difficult position. If we don't receive a definite reply from you by [date], we will have no other alternative but place our orders with another supplier. I hope this will not be necessary.

Sincerely yours,

[name]

[title]