I went through a similar discussion with a former employer years ago before I realized the futility of trying to be helpful to some people. It started with signs attempting to prohibit carry in the buildings and I learned my lesson there. Then a couple of years later they included the parking lot since it was private property and this was after the "parking lot law" had become effective. They thought they were okay since it was private property. I pointed out to them it didn't matter and showed them the statute. They said their lawyers had looked it over and they stood by their prohibition. I knew the lawyers they spoke of since I'd had interaction with them and knew what type of lawyers they were. They were not firearms or even related type lawyers and this type of thing was out of their milieu. At this time the TRSA was soliciting employers that were in violation and since mine was somewhat high profile in Texas and the DFW area and with more than 1k employees it was resolved fairly quickly after I sent them a copy of the employee policy prohibiting it. The signs were taken down and the policy was changed within a year. A few co-workers came to me and asked if I had anything to do with that and I denied it for several years until after I was gone. The ones that asked said they figured it was me, but couldn't prove it.
They are posted 30.06 &.07 and we've discussed them on this forum a few times. I did not start those threads and IIRC participated very little if at all because I was an employee at the time and tried not to be associated with them if it ever came to anything legal.