The discretion of Congress in selecting the objectives of taxation has also been held at times to be subject to limitations implied from the nature of the Federal System. Apart from matters which Congress is authorized to regulate, the national taxing power, it has been said, "reaches only existing subjects."[258] Congress may tax any activity actually carried on, regardless of whether it is permitted or prohibited by the laws of the United States[259] or by those of a State.[260] But so-called federal "licenses," so far as they relate to trade within State limits, merely express "the purpose of the government not to interfere * * * with the trade nominally licensed, if the required taxes are paid." Whether the "licensed" trade shall be permitted at all is a question for decision by the State.[261] This, nevertheless, does not signify that Congress may not often regulate to some extent a business within a State in order the more effectively to tax it. Under the necessary and proper clause, Congress may do this very thing. Not only has the Court sustained regulations concerning the packaging of taxed articles such as tobacco[262] and oleomargarine,[263] ostensibly designed to prevent fraud in the collection of the tax; it has also upheld measures taxing drugs[264] and firearms[265] which prescribed rigorous restrictions under which such articles could be sold or transferred, and imposed heavy penalties upon persons dealing with them in any other way. These regulations were sustained as conducive to the efficient collection of the tax though they clearly transcended in some respects this ground of justification. Extermination by Taxation