In the case of Houston, East and West Texas v. United States (234 U.S. 342 (1914)), a railway operated service between Texas and Shreveport, Louisiana.  They were charging less for shipments between destinations in Texas than for interstate routes.  The Interstate Commerce Commission (ICC) sued since this was a de facto tariff.  The US Supreme Court agreed with the ICC, even though it meant that the ICC could regulate the intrastate shipping rates of goods that were not leaving Texas. So basically, this case said that the Interstate Commerce Clause can be used to regulate intrastate activities, as long as there was an interstate component to the regulation as well.

The rates were set by the State of Texas, and were set that way to stop goods from Louisiana from being imported into the state.