As a side note to this...
Yes they can, just like I can have you arrested for failing to carry a concealed weapon on my land if you refuse to leave. The charge is tresspass nothing more
My small company (all three of my personalities) and 3 other employees abide by the rule. Its a condition of employment that they carry at all times when on company business unless the location they are going to prohibits it.
I wonder where I could get a sign:
"Firearms are required to enter or remain on this property, failure to be in possession of a firearm unless permission is obtained, will be considered trespassing and you may be arrested and charged with CRIMINAL TRESPASS, in accordance with Texas Penal Code Section 30.05. "