The Department of Justice filed a federal lawsuit against the State of Colorado on May 6, 2026, challenging the state's ban on large-capacity ammunition magazines as a violation of the Second Amendment [1]. The filing came one day after the DOJ sued the City of Denver over a separate firearms restriction, making Colorado the focus of two distinct federal Second Amendment actions within a single week [1].
Colorado's large-capacity magazine ban restricts civilian possession of magazines capable of holding more than a defined number of rounds. The DOJ's complaint frames the ban as an unconstitutional infringement on the right to keep and bear arms, invoking the Second Amendment as the basis for federal pre-emption of the state restriction [1]. Gun rights organizations have expressed support for the federal challenge, while gun control advocates have defended the state law as a legitimate public-safety measure within Colorado's legislative authority [2].
The lawsuit against Colorado follows the same doctrinal posture as the concurrent Denver action, suggesting a coordinated litigation strategy by the Trump administration to challenge sub-federal firearms laws through affirmative federal suits rather than through amicus participation or regulatory guidance [1]. The dual-filing approach places both municipal and state-level restrictions under simultaneous legal pressure, forcing Colorado officials to defend gun laws on two fronts in federal court [1][2].
The case will be litigated in federal district court. The governing constitutional framework is the Supreme Court's 2022 decision in New York State Rifle and Pistol Association v. Bruen, which requires courts to evaluate firearms regulations against the historical tradition of gun regulation in the United States, a standard that has produced conflicting results in lower courts reviewing magazine restrictions [1]. Colorado is expected to defend the ban as consistent with that historical tradition, and the litigation timeline will depend on whether either party seeks a preliminary injunction [2].