[Ads-l] Antedating wetback

[MULLINS, WILLIAM D (Bill) CIV USARMY RDECOM AMRDEC (US)]

OED has 1929

_El Paso [TX] Evening Post_ 22 Feb 1928 p 4 col 1 [newspapers.com]
"There's enough Mexican labor already on this side of the border to supply those demands, supplemented as it will be by those admitted annually under the quota, by those who will be permitted to cross daily  to hold regular jobs and by the "wet backs" who can't be prevented from slipping past immigration inspectors."

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