In December 2008, the American and Iraqi governments signed the U.S.–Iraq Status of Forces Agreement, which covered only American troops. It allowed them to remain in the country until 2011, but changed the status on several issues. Iraq regains sovereignty of its airspace, gains sovereignty over American contractors U.S. forces who commit crimes, if they are both off-duty and off base. The U.S. were given until July 31, 2009 to withdraw from Iraqi cities and the whole agreement was subject to a referendum of Iraqi voters held prior to June 30, 2009. If the referendum failed to approve the agreement, the Iraqi government would have given the U.S. until July 31, 2010 to withdraw completely.