In the 2010 case of CSX Transportation, Inc. v. Alabama Department of Revenue et al., the Supreme Court ruled in favor of CSX Transportation, a freight carrier company that challenged Alabama's sales and use tax on diesel fuel as discriminatory under the Railroad Revitalization and Regulatory Reform Act (4-R Act). The state imposed this tax on rail carriers but exempted their direct competitors - motor and water carriers. The court held that such an exemption constituted discrimination against rail transportation property contrary to the provisions of the 4-R Act which prohibits states from imposing taxes that discriminate against railroads. Therefore, it was determined that Alabama’s taxation system unfairly burdened CSX by taxing its purchase or consumption of diesel fuel while exempting other commercial transport entities.

In the dissenting opinion for CSX Transportation, Inc. v. Alabama Department of Revenue et al., Justice Clarence Thomas disagreed with the majority's interpretation of federal law to allow a rail carrier to challenge its tax treatment by comparing itself only to other commercial and industrial taxpayers. He argued that this narrow comparison group was not supported by the text or history of the statute in question, which he believed required a broader comparison group including all taxpayers subject to similar taxes. Furthermore, he contended that even if such a limited comparison were permissible under federal law, it should be up to state courts rather than federal ones to determine whether any alleged discrimination is justified under state law. Finally, he criticized the majority for failing to provide clear guidance on how lower courts should apply their new standard in future cases.