What state/locality is this? In many places, the fact that you are on private property doesn't get you out of observance of traffic/parking law, especially with regard to fire lanes and parking spaces for the disabled. For example, the California law reads:
No person shall stop, park, or leave standing any vehicle, whether attended or unattended, except when necessary to avoid conflict with other traffic or in compliance with the directions of a peace officer or official traffic control device along the edge of any highway, at any curb, or in any location in a publicly or privately owned or operated off-street parking facility, designated as a fire lane by the fire department or fire district with jurisdiction over the area in which the place is located.