The Parliament may by any law with respect to trade or commerce
forbid, as to railways, any preference or discrimination by any State, or by
any authority constituted under a State, if such preference or discrimination
is undue and unreasonable, or unjust to any State; due regard being had to the
financial responsibilities incurred by any State in connexion with the
construction and maintenance of its railways. But no preference or
discrimination shall, within the meaning of this section, be taken to be undue
and unreasonable, or unjust to any State, unless so adjudged by the
Inter-State Commission.