https://en.wikipedia.org/wiki/Branzburg_v._Hayes
Branzburg v. Hayes, 408 U.S. 665 (1972)
Writing for the majority, Justice Byron White declared that the petitioners were asking the Court “to grant newsmen a testimonial privilege that other citizens do not enjoy. This we decline to do.”
“Sooner or later, it would be necessary to define those categories of newsmen who qualified for the privilege, a questionable procedure in light of the traditional doctrine that liberty of the press is the right of the lonely pamphleteer who uses carbon paper or a mimeograph just as much as of the large metropolitan publisher who utilizes the latest photocomposition methods.”
I found the below guide to be very helpful:
Congressional Research Svc: Freedom of Speech and Press:
Exceptions to the First Amendment
(Prepared for Members and Committees of Congress, published 2014)
https://fas.org/sgp/crs/misc/95-815.pdf