by John Marshall Harlan, Connolly v. Union Sewer Pipe Company…
“ We must not be understood by what has been said as conceding that the question of a denial of the equal protection of the laws can never arise under the taxing statutes of a state. On the contrary, the power to tax is so far limited that it cannot be used to impair or destroy rights that are given or secured by the supreme law of the land. We only need to say, in this connection, that the constitutional validity of the statute of Illinois now before us is not necessarily to be determined by the same principles that apply to taxing laws. ”
