One Subject at a Time Act This bill requires each bill or joint resolution to include no more than one subject and the subject to be clearly and descriptively expressed in the measure's title. An appropriations bill may not contain any general legislation or change to existing law that is not germane to the subject of such bill. The bill voids measures or provisions noncompliant with these requirements, including appropriation provisions outside the relevant subcommittee's jurisdiction. Additionally, a person (individual or entity) who is aggrieved by the enforcement, or the attempted enforcement, of a law that passed without complying with this bill's requirements may sue the United States for appropriate relief.