In the 1931 case of Utah Power & Light Co. v. Pfost, Commissioner of Law Enforcement, et al., the United States Supreme Court ruled in favor of Utah Power & Light Company (UP&L). The company had challenged an Idaho law that imposed a tax on electricity generated outside the state but sold within it. UP&L argued that this violated both the Commerce Clause and Due Process Clause of U.S Constitution as they produced power in Wyoming and Utah but sold some to customers in Idaho. The court agreed with UP&L's argument stating that such taxation was discriminatory against interstate commerce and thus unconstitutional under both clauses mentioned above. This decision reinforced constitutional protections for businesses operating across state lines from potentially discriminatory local or state taxes.

In the dissenting opinion for Utah Power & Light Co. v. Pfost, Justice Stone argued that the Idaho tax law should not be invalidated on grounds of discrimination against interstate commerce. He contended that there was no substantial evidence to prove that the state's method of taxation resulted in a higher burden on out-of-state companies than those operating within its borders. The justice further stated that it is not enough to simply assert such claims without concrete proof and maintained that any differences in tax burdens could be due to factors other than discriminatory intent or effect, such as variations in property values or business operations across states.