Suppose Mike's Bikes, a store that attracts primarily customers from the local area, is in violation of some provision of the Americans with Disabilities Act of 1990. Mike's lawyer challenges the constitutionality of the provision on the grounds that "Mike's Bikes" does not operate outside Mike's home state, nor does it sell to more than a few residents of other states.
The ADA does not explicitly cite any constitutional provision as the source of the Congressional authority to pass it. It may be presumed to be supporters by the Interstate commerce clause. During the 20th century and to the present this clause has been interpreted very broadly to grant regulatory authority over almost any economic activity in the US. An early and leading case on this point was Wickard v Filburn 317 U.S. 111 (1942). In this case regulation under the Commerce Clause of the planting and harvesting of wheat intended to be fed to livestock on the farm, and consumed by the residents thereof, but not separately marketed, was held to be proper and within the power of congress. The opinion in this case says:
(at 120) We believe that a review of the course of decision under the Commerce Clause will make plain, however, that questions of the power of Congress are not to be decided by reference to any formula which would give controlling force to nomenclature such as "production" and "indirect" and foreclose consideration of the actual effects of the activity in question upon interstate commerce.
Quoting Swift & Co. v. United States, 196 U. S. 375, 196 U. S. 398 (at page 122) the opinion further said that:
"commerce among the States is not a technical legal conception, but a practical one, drawn from the course of business."
The opinion went on to say that:
(at 124-125) That an activity is of local character may help in a doubtful case to determine whether Congress intended to reach it. The same consideration might help in determining whether, in the absence of Congressional action, it would be permissible for the state to exert its power on the subject matter, even though, in so doing, it to some degree affected interstate commerce. But even if appellee's activity be local, and though it may not be regarded as commerce, it may still, whatever its nature, be reached by Congress if it exerts a substantial economic effect on interstate commerce, and this irrespective of whether such effect is what might at some earlier time have been defined as "direct" or "indirect."
(at pages 127-128) That appellee's own contribution to the demand for wheat may be trivial by itself is not enough to remove him from the scope of federal regulation where, as here, his contribution, taken together with that of many others similarly situated, is far from trivial.
(at pages 128-129) Congress may properly have considered that wheat consumed on the farm where grown, if wholly outside the scheme of regulation, would have a substantial effect in defeating and obstructing its purpose to stimulate trade therein at increased prices.
None of the cases under the ADA that I have found challenge the congressional power to pass the act. In the Wikipedia article on the act, it is said to be largely based on the scheme of Section 504 of the Rehabilitation Act of 1973. I there were serious question as to the Congressional power to pass such laws, i would have expected a challenge to have been litigated in that time.