ATR-42 Captain reported maintenance instructed crew to do unsafe procedures and failed to help disconnect GPU.

Narrative

On the above time and date after engine start I requested the GPU be removed. Soon after; the ground personnel sent me a note stating it wasn't disconnecting. I left the cockpit and handed the controls to the First Officer to see what was wrong. After talking to them and finding a large exposed copper in the GPU line I had thought it could have shorted the GPU and soldered itself in place. I called for me through Operations and also called Maintenance Control to let them know about the situation. I spoke to Name and have never had such a belittling conversation with another adult. Extremely unprofessional and very concerning that he is who pilots turn to when they need guidance on a maintenance event. Once I told him I was writing up the aircraft he hung up the phone. While swapping aircraft I received a call from my First Officer. He said that Maintenance was telling me I needed to clear my discrepancy in the log book with EIE (entered in error). When I made it to the plane Maintenance was waiting for me and told me to EIE my write up. I refused and told him the aircraft was not airworthy due to the GPU still being connected. He asked a few more time and I refused every time. The GPU was later removed with an MEL. This is the second incident in two weeks where I have had Maintenance asked me to do procedures and/or operate outside of our safety culture. However in both incidents I did call our Chief Pilot and he backed me fully with my stance. I'll be filing another report tomorrow over a fueling incident where they wanted me the pilot to do a maintenance procedure on the aircraft in which I refused also.