From the “The past isn't dead, it isn't even past” dept., via Jill Lepore's “These Truths: A History of the United States”:

After the Chinese Exclusion Act of 1882, large growers had turned to Japanese laborers, but a so-called gentleman's agreement between Japan and the United States ended their migration in 1908, after which growers began sending employment agents over the border and into Mexico to recruit workers. In an era when the regime of scientific management maligned Hungarians, Italians, and Jews as near-animals who needed to be ruled not by the lash but by the stopwatch, business owners and policymakers tended to describe Mexican immigrants—desperately poor political refugees—as ideal workers. In 1908, U.S. government economist Victor S. Clark claimed that Mexican immigrants were “docile, patient, usually orderly in camp, fairly intelligent under competent supervision, obedient and cheap,” and, in 1911, a U.S. congressional panel reported that while Mexicans “are not easily assimilated, this is not of very great importance as long as most of them return to their native land after a short time”...

This did not quiet nativists, the American Eugenics Society warning: “Our great Southwest is rapidly creating for itself a new racial problem, as our old South did when it imported slave labor from Africa. The Mexican birth rate is high, and every Mexican child born on American soil is an American citizen, who, on attaining his or her majority, will have a vote. This is not a question of pocketbook or of the ‘need of labor’ or of economics. It is a question of the character of future races. It is eugenics, not economics.” Congress, pressured by eugenicists and southern and western agriculturalists, in the end exempted Mexicans from the new immigration restriction regime, while also requiring not only passports but also visas for anyone entering the United States. Thus it erected hurdles that allowed Mexicans to cross the border to work temporarily but denied access to citizenship.