Take time to step back from the situation and evaluate it objectively. Consider the perception of the person who gave the reprimand. Try to understand that person's point of view as much as possible before writing your objection. If you react immediately, without taking time to think it over, you risk coming across as being upset and defensive. Try to be calm and think logically.
Address your letter to someone who has the ability to understand your point of view and the power to take action. Consider writing to the supervisor of the person who issued the reprimand, or to the human resources department. Getting a fair hearing for your letter is important if it is going to change anything about your work situation.
Write in a tone that is respectful, not forceful and angry. This letter will most likely end up in your personnel file, and it will be there for others to see for a long time.
Acknowledge and take responsibility for any wrongdoing or bad behavior on your part. Avoid placing blame on the person who gave the reprimand, or on anyone else.
Focus your letter's contents on facts and observations. Refrain from emotional outbursts. This will make the letter's reader more likely to pay attention to what you have to say.
Briefly and concisely state your case or tell your side of the story. Keep your letter less than a page in length. Otherwise, you run the risk of sounding like a whining employee with a big chip on your shoulder.
Ask someone else who is not involved in the situation to read your letter before you send it. That person can help provide perspective on the situation and give you an objective opinion of how your response comes across.