If you learn through the office grapevine that a colleague is talking poorly about you, you're likely to react with a mix of anger and alarm. That's particularly true if the criticisms are unfounded and unwarranted. Stop the behavior in its tracks and prevent your name from being further tarnished by confronting the employee and getting to the bottom of the issue.
Get the Facts
Don't confront a colleague about bad-mouthing you until you're sure he's really doing it. Gather information like notes, emails or firsthand accounts of his criticisms from colleagues or other reputable sources. For example, your secretary might tell you a client came by to see you, but was intercepted in the waiting room by one of your colleagues. The colleague was overheard telling the client you’re unreliable and that you always keep people waiting. Now that you have proof and a witness, you can take the next step of speaking with your colleague.
Talk to the Colleague
Speak privately with your colleague and tell him what you heard. Be calm and professional and stick only to the facts. For example, you might say, "A trusted source overheard you telling Tom Smith I’m unreliable. Is this true?” This approach is straightforward and puts the onus on your colleague to confirm or deny his behavior. If he denies the charge, say, “Why would someone tell me that?” His response will give you an indication of how best to proceed.
Your colleague might try to back out of the confrontation by saying he was misunderstood or was just joking with your client. If this is the first time you've had a run-in with this colleague, give him the benefit of the doubt that his comments were more about poor judgment than maliciousness. Explain to him that such behavior might diminish your client’s faith in the company, which is damaging to all of you. If this isn't the first time you've caught the colleague bad-mouthing you, bring that fact to his attention and tell him you want the issue resolved by corporate mediation.
Your colleague might own up to his comments and instigate a verbal altercation by admitting to talking poorly about you, justifying his actions by saying you left the client waiting, which is a bad representation of the company. You can either defend your actions and explain the circumstances, or assume that your colleague has underhanded or ulterior motives for his behavior and take the issue to a higher authority.
Talk to your immediate supervisor or your human resources representative about conflict resolution. This might involve a joint discussion with HR, your department manager or an in-house mediator. Explain your colleague’s behavior and describe how you tried to resolve the issue yourself. While bad-mouthing you is unprofessional, if there's any truth to what the colleague is saying about your performance, be prepared to defend yourself during the mediation session.