(COMMON DREAMS) Lauren McCauley — America’s Fortune 500 companies are “playing by different rules” when it comes to the federal tax system and, according to a new report out Tuesday, are stashing $2.1 trillion in offshore tax havens—with as much as $620 billion owed to the U.S. taxpayers who are left footing the bill. The report, Offshore Shell Games 2015: The Use of Offshore Tax Havens by Fortune 500 Companies (pdf), examines the accounting tricks that have enabled the country’s most profitable companies to hide their earnings.