Foreigner citizens have no (literally none) Fourth Amendment protection while outside the U.S. AFAIK there's no other specific provision in the Constitution (even as amended) speaking to communications privacy.
Even assuming the Fourth Amendment does apply, the "third-party doctrine" that has been applied to the Fourth Amendment since the 19th century would open up a hole for foreign surveillance large enough to drive a truck through, when applied to telecommunications. This hole was closed by Congress for telephones, pagers, cell phones and some other things, but not for email or other Internet traffic.
Even if Congress did pass a law restricting interception of Internet traffic, Congress could make exceptions to their own law... such as FISA and the FISA Amendments Act. Also, many other laws restricting the ability of government to wiretap have specific exceptions for the purpose of foreign surveillance.
It might be arguable that FISA Amendments Act goes too far in the leeway it gives regarding how to decide whether a targeted individual is a U.S. person or not, but that wouldn't substantially affect the law as implemented (and wouldn't make any of the non-Americans feel better either way).
