If you're dealing with a co-worker whose behavior is bad enough to warrant a complaint, get your complaint written as soon as possible and in the hands of the people who can help. As with any business correspondence or complaint letters, the letter should state the facts without resorting to name-calling or emotional statements.
Examine Workplace Protocols
Look over your employee handbook before you start writing, to find out if there's already a protocol in place for co-worker complaints. In some cases there's an internal form you'll need to fill out, or you'll be instructed to direct the letter to a particular person within the company. Sometimes that's your direct supervisor, but it may also be the company's human resources officer. If the problem involves something illegal, such as sexual harassment or illegal activity, document all incidents you've witnessed, in case you need to share that information later.
Review the Problem
Before you write, also think about what the addressee is going to be concerned about -- which in most cases is the health and productivity of the business. If the co-worker is engaging in annoying behaviors, it's not enough to tell the addressee that your co-worker is doing something annoying. Instead, write about how that annoying behavior affects you or the workplace. If it makes it difficult for you to complete your work in a timely fashion, for example, that's going to affect the company's overall productivity. If you review the problem and find that the co-worker's behavior isn't actually affecting the company's productivity or overall health, you might actually discover that the complaint letter is unnecessary, reminds business management expert Alison Green of U.S. News & World Report.
State the Facts
Start off the letter with something like "I am writing to inform you of a problem that is affecting the productivity of the office." This will get the addressee's attention. Then state the facts of the problem, providing enough detail to give the addressee an idea of what's going on, but not so many details that she'll get bogged down. Also focus on "I" statements, suggests Your Office Coach Marie G. McIntyre, talking about how the problem affects you instead of talking only about the co-worker's behavior. Keep this section to one or two paragraphs; a concise account of the problem is the best way to go, says Green.
Ask for a Resolution
In the final paragraph of the letter, discuss what you've done to try to fix the problem. If you've talked with the co-worker personally, for example, mention it. Then ask for the addressee's help in fixing the problem. This is preferable to a demand, as it will appear less like tattling and more like you're looking for a collaborative solution. At the end, sign the letter cordially, and include a date on the top or bottom so there's a definitive record of when you tried to get the problem solved. In the best-case scenario, your boss or human resources officer will take care of the problem from there.