William O. Douglas

“ A patent empowers the owner to exact royalties as high as he can negotiate with the leverage of that monopoly. But to use that leverage to project those royalty payments beyond the life of the patent is analogous to an effort to enlarge the monopoly of the patent by tieing the sale or use of the patented article to the purchase or use of unpatented ones. ”

“ The exaction of royalties for use of a machine after the patent has expired is an assertion of monopoly power in the post-expiration period when, as we have seen, the patent has entered the public domain. ”

“ In light of those considerations, we conclude that a patentee's use of a royalty agreement that projects beyond the expiration date of the patent is unlawful per se. If that device were available to patentees, the free market visualized for the post-expiration period would be subject to monopoly influences that have no proper place there. ”