You will rarely get along with every individual in your workplace, as any workplace is a mix of different personalities and experiences. Sometimes a personality mismatch with a co-worker can escalate into a genuine conflict, and these conflicts must be resolved if the company is going to run effectively. In severe circumstances, a supervisor might ask for a letter that explains your side of the story in case the matter needs to be formally addressed. These sorts of complaint letters must be handled carefully and professionally to be credible.
Insert a piece of company letterhead into your printer. This letter will become an official piece of your employee record, and well as your colleague's record, so it must look professional.
Type the date. Skip a line space. Type your supervisor's name and title, the company name, and the company address. Skip an additional line space.
Type "Dear Ms./Mr. (Name)" followed by a colon, as appropriate for your boss or the relevant human resources officer. Skip a line space.
Tell your supervisor that you are writing in regard to a conflict with your colleague, and name the colleague specifically. Give relevant details immediately, such as when the conflict began and why.
Describe the less important details of the conflict in subsequent paragraphs. Do not mention petty details such as every slight, but give the main description of the ongoing nature of the conflict. Maintain a professional, factual tone and avoid attacking your colleague in the letter. Attacks, however justified they may be, will make you look unprofessional.
Give a final evaluation of the situation in the last paragraph. If you have guilt in the disagreement, admit to it. Suggest a possible way to resolve the conflict, and indicate your willingness to work towards a harmonious outcome. For example, you might suggest a mediation session, or offer to take up work on a project that would bring you outside of the realm of daily contact with your colleague.
Type "Sincerely," or another professional closing statement and skip three line spaces. Type your full name and title. Print the letter and sign in the space above your name.
Retain one copy of the letter for your records and mail, e-mail, or hand deliver another copy to your boss.
Unless circumstances are extremely dire, it is usually best to write a formal complaint letter only when requested. Because the letter will become part of your permanent employee file, frivolous or emotion-laden letters may reflect poorly on you later on down the line. Always try to resolve conflicts in person before appealing to a supervisor in a letter.