Over its 200-year history, the federal False Claims Act (“FCA”) has saved the federal government billions of dollars in false claims for payment. But one type of false claim remains off limits in federal courts. A provision of the federal FCA known as the “tax bar” prohibits suits based on failure to pay federal taxes. See 31 U.S.C. § 3729(d). Whistleblowers who uncover federal tax fraud are limited to the Internal Revenue Service’s whistleblower program.