Here are two sources. I think, Danilo, that the idea is much older
than one might think.
Rogerson, Richard. (1997) "Theory Ahead of Language in the Economics
of Unemployment." The Journal of Economic Perspectives. 11 (1): 73-92.
Santoni. C. J. (1986) 'The Employment Act of 1946: Some History
Notes." Federal Reserve Bank of St. Louis Economic Review. (December) pp. 5-16.
When I teach this to principles students, I begin with a graph from
Henry Wallace's 1945 book "Sixty Million Jobs."
Best wishes
Pat Gunning