the McCarran Internal Security Act of 1950.

Answer 1

It would have been easier for us if you'd posted this with your original post.

Is anyone willing and able to explain the significance of this act of Congress, including its intent and purpose, and how the law was widely considered to be a violation of civil liberties?

These sites explain this act.

http://en.wikipedia.org/wiki/McCarran_Internal_Security_Act

http://writing.upenn.edu/~afilreis/50s/mccarran-act-intro.html

http://www.spartacus.schoolnet.co.uk/USAinternal.htm