The issue focused on whether the federal government should continue to collect on federal income taxes owed to the state of California for tax years beginning in 2009, when California enacted a law that required states to collect income taxes in the amount of their state sales and income tax rates.

Under California's income tax law, the state collected about $4 billion in federal taxes in fiscal year 2011, but it did so at a much higher rate than federal law requires it to collect. The federal law, signed by President Obama on