If your co-worker is consistently late, slacks off, or helps himself to office supplies from the storeroom, it might leave you feeling frustrated, irritated or even angry. It's often difficult to deal with a co-worker's poor work ethics; however, you don't necessarily have to ignore your concerns. To determine how you should react, you need to assess the situation and do what you feel is best to maintain your own strong work ethic.

Address Your Concerns

No one wants to come across as a goody two-shoes, but there's usually no harm in addressing your concerns directly with your co-worker in a polite, professional manner. Keep in mind that as an employee, you play a crucial role in helping to maintain an ethical workplace, according to the "Ethics in the Workplace" a brochure from the HR Hero website. When you see a colleague acting in an unethical manner, ask to speak with him privately. Never confront a colleague in front of other co-workers, as this can only lead to humiliation and embarrassment. Explain your concerns and ask him if he is willing to change his behavior. There's no guarantee that he will be open to hearing your concerns, but it's worth the effort.

Speak to Your Boss

You also don't want to come across as a tattletale, but speaking with your supervisor might be a helpful way to address your concerns, notes Simon Gibson, who writes the syndicated column, Office Politics 101, which is dedicated to human resources management and appears in British Columbia newspapers as well as online. The chances might be good that your supervisor is already aware of your co-worker's unethical behavior, but he might tolerate it for certain reasons. Perhaps she is a hard worker even though she comes in late, or maybe she has personal issues of which you're unaware. Don't be catty or hurtful; stay focused on the specific concern or problem. Talking to your supervisor in a professional manner provides him with the opportunity to address your concerns and shows that you are dedicated to the success of your workplace.

Turn a Blind Eye

Ignoring your co-worker's unethical behaviors might sound like the last thing a responsible and dedicated person should do. But sometimes -- depending on the specific behavior -- it might be best to let your co-worker create her own destiny. You shouldn't allow yourself to obsess over your co-worker's bad work ethics to the point where his behavior begins to affect your work. In some situations, it's more important to focus on your own performance and make sure that you're doing a good job -- unless your co-worker's behavior is affecting your work -- notes Tim Holdsworth, business analyst and marketing specialist for AlignTech Solutions. Eventually, your supervisor or someone else will pick up on -- and hopefully address -- her behavior.

File a Complaint

Filing an official complaint about your co-worker's unethical behavior could depend on the type of work you perform or the specific behavior. For example, the code of ethics of certain professions, like medicine, psychology or social work, usually includes a clause about reporting a colleague's unethical behaviors, especially if the behavior could cause harm to a patient or to the public. If you're not sure of whether you should file an official report or complaint, you might want to speak to your union representative or an official from your professional board, if applicable.