Washington state constitution
Article XII
Section 15

No discrimination in charges or facilities for transportation shall be made by any railroad or other transportation company between places or persons, or in the facilities for the transportation of the same classes of freight or passengers within this state, or coming from or going to any other state. Persons and property transported over any railroad, or by any other transportation company, or individual, shall be delivered at any station, landing or port, at charges not exceeding the charges for the transportation of persons and property of the same class, in the same direction, to any more distant station, port or landing. Excursion and commutation tickets may be issued at special rates.