Dear …
__(Name of Organization)__ has recently had a change in management and ultimately we are now adopting changes to some of our current business practices. Overall, it is a positive direction for our organization, however, there are some adverse affects to some of our existing __(business/vendor)__ relationships. Regrettably, __(Name of Organization)__ will no longer be utilizing the services of __(name of Company)__. The decision has been made that this change will be effective __(date/immediately)__.
Please allow me to assure you that this in no way reflects the quality of services we received from your company. We were always happy with the __(-type-service/products and service)__ __(Name of company)__ provided and it was a pleasure dealing with you. It is most unfortunate that this turn of events has determined the end our business relationship at this time. As difficult as this news may be, we hope that you can understand that it is strictly a business decision.
Thank you for all your past service, __(Name)__. We wish you and __(name of company)__ all the best.
Yours truly,