not sure if this is what you're talking about but in 1942 the US and Mexico signed the Mexican Farm Labor Agreement which guaranteed decent living conditions (sanitation, adequate shelter, food) and a minimum wage (30 cents an hour) for Mexican migrant workers under the Bracero Program
this was partly due to the labor shortage caused by WWII
if not, maybe this would help: during an earlier period in US history, nativism mixed with strong anti Chinese sentiments led to the Chinese exclusion acts; However, despite some murmurs of anti Hispanic sentiment as well, there was never the same kind of push to actually kick Hispanics out of the country bc ultimately big farm owners and others relied on them as a labor supply