The Commissioner of Transportation shall make a special investigation as to the condition of the fences on the line of any railroad, when so requested in writing, and, if the commissioner deems it necessary, shall issue an order directing the company operating such railroad to erect or repair such fences. Such order shall specify the place or places at which, the manner in which and the time within which the fences are to be erected or repaired and shall be served upon the company. Such service may be made by mailing a registered or certified letter addressed to the secretary of the company.