Employment is "at will" in Texas, and unless such a bill gets passed, and employer has the right to bar employees from having guns stored in their vehicles on company property. It doesn't matter if your company's customers also use this lot. The lone exception would be if the lot were shared with other businesses. For instance, if you work at a supermarket where other stores also use the same parking lot, then your employer could not bar you from storing a weapon in your car on that lot, since it is not exclusively company property.