In Katzenbach v$.$ McClung the U$.$S$.$ Supreme court ruled:

Since McClung purchased over $\frac{1}{3}$ of the restaurant's supplies from distributors who at some point were interstate, McClung was subject to the federal regulation based upon the commerce clause of the U$.$S$.$ Constitution.

Since McClung had business that was purely local, the commerce clause of the U$.$S$.$ Constitution did not apply in this case.

Since McClung allowed "colored" people to buy takeout in the back of the restaurant but not sit down with "white" folks inside, the commerce clause of the U$.$S$.$ Constitution did not apply since this was not considered commerce.

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