plenary power

Plenary power refers to complete and exclusive authority over a particular subject matter, constrained only by constitutional limitations. When a governmental body holds plenary power, it may legislate or act within that area without requiring additional authorization. The term frequently describes Congress’s power under the Commerce Clause, Article I, Section 8, Clause 3 of the U.S. Constitution, which grants Congress broad authority to regulate interstate commerce. The Supreme Court has likewise recognized Congress’s plenary power over immigration, including the admission and exclusion of non-citizens, as affirmed in Kleindienst v. Mandel, 408 U.S. 753 (1972).

[Last reviewed in November of 2025 by the Wex Definitions Team] 

Keywords

• constitutional law

Wex

• CIVICS
• the Constitution
• wex definitions
• constitutional law
• government