My question involves labor and employment law for the state of: Georgia
I hope this is the correct forum subsection for this question, and if not feel free to move to a more appropriate section.
I work in the corrections field as a state employee and was recently promoted to a mid level supervisory role. Since being promoted I was awarded an assistant shift supervisors position working under the main shift supervisor who is one pay grade above me. On the two days that my supervisor has off each week, I am the shift supervisor and entrusted with running things in their absence.
I am having an issue with my supervisor, where the individual will call in - while off the clock and off duty and attempts to give orders/directives on their off days. I have addressed this with the director of the facility that I work at and the supervisor in question was told to back off and trust my decision making abilities due to my qualifications, work knowledge and appointment to this trusted position. I am empowered to make all decisions in my supervisors absence. Since going to my director about this, the supervisor continues to call in and attempts to micro-manage things when they are not there. I am now in a position of being written-up for insubordination due to not being able to follow a certain directive due to the fluidity of things in a correctional setting. I have 7 years with this department, and this attempted write-up could get me fired and/or affect the long term promotional aspects of my career with this organization.
I have worked for the US Military and one other state agency in my lifetime, and I have never been subjected to this level of micro-management; where an off duty supervisor will call in and try to run things. I have went over our departments work policy with a fine tooth comb and cannot find any information that would even remotely hint at expanding the ministerial or discretionary powers of a supervisor in this manner when in an off-duty status.
I'm really not certain what my question would be other than to inquire whether this is more of a departmental issue, or if there are actual guidelines(state or federal) that exist by which the authoritive scope of off-duty personnel is defined. I feel this write-up is unjustified and I need to know how to protect myself if it escalates towards possible termination on my behalf.
Any input is greatly appreciated.

