On September 21, 2007, respondents George W. Davis and Catherine V. Davis filed their brief in Davis v. Kentucky Department of Revenue of the Finance and Administration Cabinet, urging that the U.S. Supreme Court affirm a Kentucky appellate court's early 2006 ruling holding unconstitutional a statute that exempts from Kentucky's income tax interest on municipal bonds issued by Kentucky issuers while taxing interest on municipal bonds issued in other states. The brief on behalf of the Kentucky taxpayers, who paid Kentucky income tax on their out-of-state municipal mutual fund holdings, lists nine different law firms as co-counsel, including Bingham McCutchen as counsel of record and various plaintiffs' class action firms. Whereas eight amicus briefs were filed in support of the State of Kentucky's position, one amicus brief was filed in support of the Davises' brief, by the Tax Foundation, a nonprofit research organization that advocates on tax policy issues.