In the case of Heart of Atlanta Motel v. United States (379 U.S. 241 (1964), a motel in Georgia was
accused of racial discrimination, (a violation of the 1964 Civil Rights Act).
The motel argued that the law shouldn't apply to them because they weren't engaged
in interstate commerce and were therefore beyond the reach of the Interstate
Commerce Clause. However, the US Supreme Court found that the Act
was constitutional.
The Court reasoned that the motel
serviced a large number of interstate clients, and therefore it was
engaged in interstate commerce.
In addition, discrimination in
the hotel industry affected the interstate commerce involved with the
vacations and business trips of black travelers nationwide.
The Court found that,
"the power of Congress to promote interstate commerce also includes
the power to regulate the local incidents thereof including local
activities in both the State of origin as well as the destination, which
might have a substantial and harmful effect upon that commerce."