How do you handle a coworker who acts like they’re your manager?

One frustrating situation in the workplace is dealing with someone who isn’t your manager but behaves like they are. They start assigning direction, overriding decisions, or speaking with authority that doesn’t match their role. At first, it can be hard to know how to respond without creating unnecessary conflict. In most cases, the first step is to stay grounded in your actual responsibilities. Focus on doing your work clearly and consistently, and avoid letting informal “authority” from a peer change what you are accountable for. It also helps to be clear about roles when needed. If someone tries to redirect your work in a way that doesn’t align with the project structure, calmly clarifying responsibilities in meetings or conversations can prevent confusion early. A lot of workplace tension comes from blurred boundaries rather than intentional overreach. If the behavior continues and starts affecting collaboration or productivity, it may be necessary to address it more directly or involve a manager. HR can also be appropriate depending on how disruptive it becomes. The important thing is not allowing informal control to replace actual organizational structure. In most workplaces, authority only works when it’s clearly defined. When people start acting outside of that structure, it eventually becomes visible, but waiting too long can make the situation harder to correct.