Reading about The Bracero Program seems kind of wild in today's anti-immigrant US climate.
The Bracero Program (from the Spanish term bracero [bɾaˈse.ɾo], meaning "manual laborer" or "one who works using his arms") was a U.S. Government-sponsored program that imported Mexican farm and railroad workers into the United States between the years 1942 and 1964.
Temporary agricultural worker visas are one of the types of work visa with no limit, and actually have more protections than a lot of regular US workers. They still hire illegals because illegals are cheaper.