my employee keeps challenging my expertise

This post was written by Alison Green and published on Ask a Manager .
A reader writes:
I’m a manager at a small advertising start-up that has a very open and transparent culture. I actively encourage my team to challenge and disagree with me, but I’m having issues with one of them doing so in a way that I perceive as disrespectful. He frequently disagrees with me, which is fine, but he does so in a way that I think challenges my authority.
For example, if I explain a standard procedure that we’ve agreed upon and done in the past that he doesn’t remember, he’ll bluntly state, “No, we’ve never done it that way” in front of the rest of the team. This sometimes leads to us going back and forth about whether or not a fact is a fact, even when I have documentation that proves I am correct, because he can’t accept the possibility that he might be wrong.
So far, I’ve mostly been trying to ignore him when he does this: to briefly explain the facts and reference the documentation and move on, rather than to sink to his level and have it escalate to me reprimanding him. I’m not sure at what point this calls for some kind of intervention, though. Does it make me look weaker to ask him to disagree with me more respectfully in front of the rest of the team? And how do I ask him to cut it out without also discouraging the rest of the team from being open with me?
I answer this question — and three others — over at Inc. today, where I’m revisiting letters that have been buried in the archives here from years ago (and sometimes updating/expanding my answers to them). You can read it here .
Other questions I’m answering there today include:

Employee keeping using astrology to analyze coworkers
Well-meaning people keep offering me condolences … and it’s a lot
How to encourage someone you’re rejecting

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