“ We thus conclude that § 301 (h) definitely proscribes the giving of a false guaranty to one engaged wholly or partly in an interstate business irrespective of whether that guaranty leads in any particular instance to an illegal shipment in interstate commerce. Such a construction is entirely consistent with the interstate setting of the Act. A manufacturer or processor ordinarily has no way of knowing whether a dealer, whose business includes making interstate sales, will redistribute a particular shipment in interstate or intrastate commerce. ”

“ The commerce clause of the Constitution is not to be interpreted so as to deny to Congress the power to make effective its regulation of interstate commerce. Where that effectiveness depends upon a regulation or prohibition attaching regardless of whether the particular transaction in issue is interstate or intrastate in character, a transaction that concerns a business generally engaged in interstate commerce, Congress may act. ”

“ It is true, of course, that the guaranty referred to in § 303 (c) (2) is one given for the purpose of protecting the dealer 'in case of an alleged violation of section 301 (a) ,' thereby relieving him of liability if he reships adulterated or misbranded goods in interstate commerce. But where such a guaranty, as in this case, is given to a dealer regularly engaged in making interstate shipments and who may therefore have need of the guaranty, § 301 (h) imposes liability on the guarantor if that guaranty turns out to be false. ”