We have frequently asked you to demonstrate greater effort and greater commitment to your work. We gave you numerous chances to improve your performance and to meet the company's required standards. Your recent work has not been complete or accurate, however, and it is unacceptable.
Because of your poor performance, [Company name] has decided to remove you from your position as a [job title]. If you feel that we have made this decision based on insufficient knowledge, then please feel free to speak with me immediately. I will review any personal information that you provide as I deem necessary.
I wish you luck in your future endeavors.