The physician protection racket case is put forward by Nobel Prize in Economics laureate Angus Deaton and his wife Princeton economist Anne Case in their 2020 book Deaths of Despair and the Future of Capitalism: https://press.princeton.edu/books/hardcover/9780691190785/de...
Discussion of physician protectionism is also found in the 2017 book by John Hopkins political science professor Steven Teles and Niskanen Center vice president Brink Lindsey The Captured Economy: https://global.oup.com/academic/product/the-captured-economy...
This AMA/ACGME protection theory is covered by Yascha Mounk at https://www.persuasion.community/p/deaton and elsewhere.
Discussion of physician protectionism is also found in the 2017 book by John Hopkins political science professor Steven Teles and Niskanen Center vice president Brink Lindsey The Captured Economy: https://global.oup.com/academic/product/the-captured-economy...
The New York Times covered the AMA's lobbying in this 1986 article: https://www.nytimes.com/1986/06/14/us/ama-board-studies-ways...
There's also the 1970 article by University of Chicago economics professor Reuben A. Kessel, The A.M.A. and the Supply of Physicians: https://scholarship.law.duke.edu/lcp/vol35/iss2/4/