Operation Wetback was a repatriation project of the United States Immigration and Naturalization Service to remove illegal Mexican immigrants ("wetbacks") from the Southwest. During the first decades of the twentieth century, the majority of migrant workers who crossed the border illegally did not have adequate protection against exploitation by American farmers. As a result of the Good Neighbor Policy, Mexico and the United States began negotiating an accord to protect the rights of Mexican agricultural workers. Continuing discussions and modifications of the agreement were so successful that the Congress chose to formalize the "temporary" program into the Bracero program, authorized by Public Law 78. In the early 1940s, while the program was being viewed as a success in both countries, Mexico excluded Texas from the labor-exchange program on the grounds of widespread violation of contracts, discrimination against migrant workers, and such violations of their civil rights as perfunctory arrests for petty causes. Oblivious to the Mexican charges, some grower organizations in Texas continued to hire illegal Mexican workers and violate such mandates of PL 78 as the requirement to provide workers transportation costs from and to Mexico, fair and lawful wages, housing, and health services. World War II and the postwar period exacerbated the Mexican exodus to the United States, as the demand for cheap agricultural laborers increased. Graft and corruption on both sides of the border enriched many Mexican officials as well as unethical "coyote" freelancers in the United States who promised contracts in Texas for the unsuspecting Bracero. Studies conducted over a period of several years indicate that the Bracero program increased the number of illegal aliens in Texas and the rest of the country. Because of the low wages paid to legal, contracted braceros, many of them skipped out on their contracts either to return home or to work elsewhere for better wages as wetbacks.

Increasing grievances from various Mexican officials in the United States and Mexico prompted the Mexican government to rescind the bracero agreement and cease the export of Mexican workers. The United States Immigration Service, under pressure from various agricultural groups, retaliated against Mexico in 1951 by allowing thousands of illegals to cross the border, arresting them, and turning them over to the Texas Employment Commission, which delivered them to work for various grower groups in Texas and elsewhere. Over the long term, this action by the federal government, in violation of immigration laws and the agreement with Mexico, caused new problems for Texas. Between 1944 and 1954, "the decade of the wetback," the number of illegal aliens coming from Mexico increased by 6,000 percent. It is estimated that in 1954 before Operation Wetback got under way, more than a million workers had crossed the Rio Grande illegally. Cheap labor displaced native agricultural workers, and increased violation of labor laws and discrimination encouraged criminality, disease, and illiteracy. According to a study conducted in 1950 by the President's Commission on Migratory Labor in Texas, the Rio Grande valley cotton growers were paying approximately half of the wages paid elsewhere in Texas. In 1953 a McAllen newspaper clamored for justice in view of continuing criminal activities by wetbacks.

The resulting Operation Wetback, a national reaction against illegal immigration, began in Texas in mid-July 1954. Headed by the commissioner of Immigration and Naturalization Service, Gen. Joseph May Swing, the United States Border Patrol aided by municipal, county, state, and federal authorities, as well as the military, began a quasimilitary operation of search and seizure of all illegal immigrants. Fanning out from the lower Rio Grande valley, Operation Wetback moved northward. Illegal aliens were repatriated initially through Presidio because the Mexican city across the border, Ojinaga, had rail connections to the interior of Mexico by which workers could be quickly moved on to Durango. A major concern of the operation was to discourage reentry by moving the workers far into the interior. Others were to be sent through El Paso. On July 15, the first day of the operation, 4,800 aliens were apprehended. Thereafter the daily totals dwindled to an average of about 1,100 a day. The forces used by the government were actually relatively small, perhaps no more than 700 men, but were exaggerated by border patrol officials who hoped to scare illegal workers into flight back to Mexico. Valley newspapers also exaggerated the size of the government forces for their own purposes: generally unfavorable editorials attacked the Border Patrol as an invading army seeking to deprive Valley farmers of their inexpensive labor force. While the numbers of deportees remained relatively high, the illegals were transported across the border on trucks and buses. As the pace of the operation slowed, deportation by sea began on the Emancipation, which ferried wetbacks from Port Isabel, Texas, to Veracruz, and on other ships. Ships were a preferred mode of transport because they carried the illegal workers farther away from the border than did buses, trucks, or trains. The boat lift continued until the drowning of seven deportees who jumped ship from the Mercurio provoked a mutiny and led to a public outcry against the practice in Mexico. Other aliens, particularly those apprehended in the Midwest states, were flown to Brownsville and sent into Mexico from there. The operation trailed off in the fall of 1954 as INS funding began to run out.

It is difficult to estimate the number of illegal aliens forced to leave by the operation. The INS claimed as many as 1,300,000, though the number officially apprehended did not come anywhere near this total. The INS estimate rested on the claim that most aliens, fearing apprehension by the government, had voluntarily repatriated themselves before and during the operation. The San Antonio district, which included all of Texas outside of El Paso and the Trans-Pecos, had officially apprehended slightly more than 80,000 aliens, and local INS officials claimed that an additional 500,000 to 700,000 had fled to Mexico before the campaign began. Many commentators have considered these figure to be exaggerated. Various groups opposed any form of temporary labor in the United States. The American G.I. Forum, for instance, by and large had little or no sympathy for the man who crossed the border illegally. Apparently the Texas State Federation of Labor supported the G.I. Forum's position. Eventually the two organizations coproduced a study entitled What Price Wetbacks?, which concluded that illegal aliens in United States agriculture damaged the health of the American people, that illegals displaced American workers, that they harmed the retailers of McAllen, and that the open-border policy of the American government posed a threat to the security of the United States. Critics of Operation Wetback considered it xenophobic and heartless.