The U.S. state of Illinois subsequently audited Mead's income tax returns and charged Mead an additional $4 million in income tax and penalties for the sale of LexisNexis; Mead paid the tax under protest, then sued for a refund in an Illinois state court. On April 15, 2008, the U.S. Supreme Court agreed with Mead that the Illinois courts had incorrectly applied the Court's precedents on whether Illinois could constitutionally apply its income tax to Mead, an out-of-state, Ohio-based corporation. The Court reversed and remanded so that the lower courts could apply the correct test and determine whether Mead and Lexis were a "unitary" business.