In this article, Bradley Markano, Joshua Drew, and Jason Workmaster write that in a concurring opinion in U.S. ex rel. Montcrief v. Peripheral Vascular Associates PA, Fifth Circuit Judge Stuart Kyle Duncan became the latest federal judge to challenge the constitutionality of the qui tam provisions of the False Claims Act (FCA). Judge Duncan's opinion adds to a growing list of judges and justices questioning whether it is constitutional for private parties to litigate on behalf of the government under the FCA's qui tam provisions. This issue is being closely watched, as broader acceptance of these constitutional challenges could impose major new constraints on whistleblowers and signal a sea change for FCA enforcement. In FY 2024 alone, qui tam cases accounted for over $2.4 billion of the $2.9 billion recovered under the FCA, highlighting the significant impact a change could have.