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. It has often been invoked by big government liberals who wish to give more power to the Federal Government and/or dismant states' rights.
The Supreme Court of the United States greatly expanded the reach of the clause in Heart of Atlanta Motel v. United States. The majority opinion cited Caminetti v. United States, which deemed that the interstate travel of passengers could be regulated as interstate commerce, and McCulloch v. Maryland, amongst others, to conclude that "[T]he power of Congress to promote interstate commerce also includes the power to regulate the local incidents thereof, including local activities in both the States of origin and destination, which might have a substantial and harmful effect upon that commerce".
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; in this case striking down the overarching Gun-Free School Zones Act of 1990 which was being used against a twelfth grader.
The primary legal challenge to ObamaCare is its lack of authority under the Commerce Clause.
- http://caselaw.lp.findlaw.com/scripts/getcase.pl?navby=case&court=us&vol=379&page=241, Supreme Court of the United States, FindLaw, Justice Tom Clark, Accessed April 6, 2014, Dec 14 1964, ATLANTA MOTEL V. UNITED STATES, 379 U.S. 241 (1964)