Page "Stanley Forman Reed" Paragraph 38

*" There is a recognized abstract principle, however, that may be taken as a postulate for testing whether particular state legislation in the absence of action by Congress is beyond state power.

This is that the state legislation is invalid if it unduly burdens that commerce in matters where uniformity is necessary — necessary in the constitutional sense of useful in accomplishing a permitted purpose.

"-Morgan v. Commonwealth of Virginia, 328 U. S. 373 ( 1946 )