Section 6. Every common carrier by motor vehicle shall publish and file with the department and keep open for public inspection tariffs containing all the rates and charges for transportation of property and all services in connection therewith between points on its own routes, and between points on its own routes and points on the routes of any other such carrier or on the route of any common carrier by railroad, express or water when a through route and joint rate shall have been established. Such rates and charges shall be stated in lawful money of the United States. The department may reject any tariff filed with it which is not consistent with this section and with its orders, rules and regulations under this chapter.

Every such common carrier shall establish, observe and enforce just and reasonable rates, charges and classifications and reasonable regulations and practices relating thereto, which shall become effective on a date fixed by such carrier, which shall be at least thirty days after the filing of the tariff containing the same, unless suspended by the department prior to its effective date upon complaint of any person, organization or body politic, or by the department on its own motion; provided, that a rate may be established to become effective within said thirty days in order to meet the then existing rate of any competing common carrier, in which case it may become effective upon the effective date of the rate of such competing common carrier or at any time thereafter if established thereafter, upon the filing of a tariff or supplement thereto consistent with such reasonable rules and regulations as may be prescribed by the department.

The department may establish from time to time such reasonable rules and regulations as it may deem necessary pertaining to the form of tariff schedules, the time and manner of filing thereof, the suspension of rates before the same become effective, and hearings upon the validity of any filed or existing rate.

The department, in its discretion and for good cause shown, may allow publication of rates or of changes therein, upon notice less than that herein specified, or may modify the requirements of this section with respect to posting and filing of tariffs, either in particular instances or by general order applicable to special or peculiar circumstances or conditions.

The department, upon complaint of any common carrier by motor vehicle or of any other person, or upon its own motion, after hearing, may allow or disallow any filed or existing rates and may alter or prescribe the rates of common carriers in connection with the transportation of any or all classes of property to any and all points within the commonwealth and any service connected therewith, in accordance with the legal standards provided in this chapter. Whenever, upon complaint or in an investigation on its own initiative, the department, after hearing, shall be of the opinion that any rate or charge demanded, charged or collected by any common carrier by motor vehicle, or any classification, rule, regulation or practice whatsoever of such carrier affecting such rate, charge or the value of the service thereunder, is or will be unjust or prejudicial, it shall determine and prescribe the lawful rate of charge, or the lawful classification, rule, regulation or practice thereafter to be made effective. The department shall annually establish reasonable maximum and minimum rates or charges consistent with industry and economic conditions and consistent with the declaration of policy contained in section one.

In the exercise of the power to prescribe just and reasonable rates for the transportation of property by common carriers by motor vehicle and to disallow rates filed by any such carrier, the department shall give due consideration, among other factors, to the inherent advantages of transportation by such carrier, to the effect of any rates under consideration upon the movement of traffic by such carriers, to the need in the public interest of adequate and efficient transportation service by such carriers, to the cost of service and to the need of revenues sufficient to enable such carriers under honest, economical and efficient management to provide such service.

No common carrier by motor vehicle, unless otherwise provided by this chapter, shall engage in the transportation of property upon any way, unless the rates and charges upon which the same is transported by said carrier shall have been filed and published in accordance with this chapter.