Over the past few years, a number of states have taken incremental steps to reform their corporate income taxes to curtail tax avoidance by large and profitable companies. One such reform, combined reporting, prevents corporations from using a range of accounting schemes to shift profits from one state to another in order to artificially reduce the taxes they owe. The seventeen states that now use combined reporting may eventually get some company, as two Governors - Eliot Spitzer (D-NY) and Chet Culver (D-IA) - have included provisions in their budget proposals for the coming fiscal year to institute combined reporting. To learn more about combined reporting and how it works, see the Institute on Taxation and Economic Policy's updated policy brief.
Several tax avoidance techniques are available to corporations operating in states that don't have combined reporting. For example, a recent Wall Street Journal article (subscription required) notes that Wal-Mart may have been able to avoid as much as $350 million in state corporate income taxes between 1998 and 2001 due to a loophole that could be countered with combined reporting.