Can We Discipline for Unauthorized Overtime?

Answer from Kim, SPHR, SHRM-SCP:

You may discipline for unauthorized overtime as you would for any other violation of your policy.

It sounds as though you have already given the employee a verbal warning. I would recommend issuing a written warning for the next violation. If the violations continue, you could take further corrective action, up to and including termination.

Following this sort of progressive discipline in accordance with your policy helps protect you in the event the employee challenges any of the corrective actions.

Remember, though, that any overtime worked by non-exempt employees must be compensated, regardless of whether the overtime was authorized.