In different countries, different legislation exists that regulates the extent to which authorities are allowed to use surveillance means.
In the U.S., the NSA is the most powerful intelligence agency. In addition to monitor all foreign communications, it still has the legal authority to intercept any communication that begins in the U.S., as well as use American citizens' private communications as fodder for trainee spies (according to ).
The same article reports that there is a way to circumvent the prohibition on spying on the own population. UKUSA partners (see 2.1) have used each other several times to intercept communications in their countries. After finding useful results, these data were passed back to the requesting authority.
According to a reference in , Norway, for example, has an interesting standpoint: the Norwegian defense department sees no reason to comment on Echelon since it is designed to intercept civilian traffic, and thus it is not a military issue.