On December 9, 2014, the Supreme Court heard oral argument in Alabama Department of Revenue v. CSX Transportation. The question presented in the case is twofold: (1) whether a state violates the Railroad Revitalization and Regulatory Reform Act of 1976 (4-R Act) by “discriminating against a rail carrier” when it requires rail carriers to pay a sales-and-use tax but exempts railroads’ competitors from paying the same tax; and (2) whether, in resolving a claim of unlawful tax discrimination under the 4-R Act, a court should consider the state's broader tax system rather than focusing only on the challenged tax provision. -- To discuss the case, we have Andy Grewal, who is an Associate Professor of Law at the University of Iowa College of Law.