Commercial property owners can post the appropriate signage on the property regulating the parking and towing of abandoned vehicles in accordance with Idaho Statute 49- 1806. This code says:
Any person having possession or control of real property who finds an unauthorized vehicle standing upon his property is permitted to have the vehicle removed if there is posted on or near the property in a clearly conspicuous location, in large print, a sign or notice that unauthorized vehicles will be removed at the owner's expense and designating the name of the towing firm.
It is against the law to call a tow company and have a vehicle towed off your commercial property unless you have a standing contract and visible signage posted conspicuously on your property.
Anyone having possession or control of commercial real property will be responsible for posting the appropriate signage and towing of any vehicles. Most all Tow companies will provide the signage and the service at little or no charge. Contact a tow company to set up a contract and have them post signs on your property to let violators know that #1 their car will be towed if left without permission and #2 where their car was towed if they violated your parking regulations.