Idaho constitution
Article XI
Section 18

That no incorporated company or any association of persons or
stock company, in the state of Idaho, shall directly or indirectly combine or make
any contract with any other incorporated company, foreign or domestic, through
their stockholders or the trustees or assignees of such stockholders, or in any
manner whatsoever, for the purpose of fixing the price or regulating the production
of any article of commerce or of produce of the soil, or of consumption by the
people; and that the legislature be required to pass laws for the enforcement
thereof, by adequate penalties, to the extent, if necessary for that purpose, of the
forfeiture of their property and franchise.