Seeing as we passed a law giving the government the right to spy on everyone, I'd say that one (all internet communication crossing the border, such as communicating with most email servers, or for that matter most any site I can think of, and telephone conversations).
I don't think they actually spy on everyone all the time, since that'd require far too much resources, and I think they especially leave me alone, because I can admit that I'm not that interested. But they do have the ability to, and they probably check in randomly from time to time, while looking for something they're interested in.