Commerce Clause
From Conservapedia
The Commerce Clause is the provision in the U.S. Constitution that establishes the power of Congress to regulate commerce among the states and with foreign entities. It is set forth in Article I, Section 8, Clause 3.
This is one of the most important, and most-often litigated, clauses in the U.S. Constitution. It is the single most important source of power for Congress, and has been bused by it to pass laws governing business, civil rights, abortion and other social areas. Only beginning in 1995, in Lopez v. United States, did the Rehnquist Court begin to limit the scope of what Congress might do based on this clause.
