No motor common or contract carrier of passengers or household goods shall charge, demand, collect, or receive a greater or lesser or different compensation for the transportation of passengers and property or for any service rendered in connection therewith than the rates, fares, and charges prescribed or approved by order of the commissioner; nor shall any such motor carrier unjustly discriminate against any person in its rates, fares, or charges for service. The commissioner may prescribe, by general order, to what persons motor common and contract carriers of passengers or household goods may issue passes or free transportation; may prescribe reduced rates for special occasions; and may fix and prescribe rates and schedules.