Work at Premises of Shippers and Consignees. (a) Loading or unloading by hand of trucks, trailers, vans, or any other type of equipment used as a truck, trailer or van, shall be performed only by persons employed under this Supplemental Agreement and, in particular, employees of any company not party to this Supplemental Agreement shall not load, unload by hand, or enter any such equipment for that purpose. The only exceptions to this paragraph are: