Due to the increase in raw material costs， we must unfortunately raise the cost of our merchandise to you.

　　We have avoided raising our prices for as long as possible， but we can no longer prolong the inevitable¹. We have enclosed our new price list for your review which goes into effect on   [date]   Any orders placed between now and [date of increase] will be honored at the lower prices.

　　We wish to thank you for your valued account and know that you will understand the necessity for this price increase.