Once again with the "spying on citizens" meme...
Look: citizenship is not the point. It's right there in the constitution: "... nor deny to any person within its jurisdiction the equal protection of the laws".
If a person is within your jurisdiction, they're protected by the same laws, whether they're a citizen of Kansas or Karachi. Conversely, if they're not within your jurisdiction, then they're not protected by your laws, because that's basically what "jurisdiction" means.
No act of Congress can make it legal to spy on foreigners, without also making it legal to spy on Americans in the same circumstances. That law would be, quite simply, unconstitutional.