"The following commentary by James G. Hudec is a response to 'Recollections of the Church committee's Investigations of NSA [National Security Agency],' by L. Britt Snider. In his article, Mr. Snider, who in 1975 was counsel on the staff of the Church committee, described the Congressional concern over NSA's SHAMROCK operation, which involved NSA's screening of some international telegrams leaving the United States for foreign destinations. Under the program, according to press allegations, NSA was reading telegrams sent by US citizens."
Center for the Study of Intelligence: https://www.cia.gov/library/center-for-the-study-of-intelligence/index.html
Studies in Intelligence (Winter/Spring 2001), no.10, p.85-94