About half of U.S. crop workers are living undocumented in the country and more than two-thirds are foreign-born, according to the most recent figures from the U.S. Department of Labor's National Agriculture Workers' Survey.

Many farmers say they cannot find U.S. citizens willing and able to do the strenuous jobs they need to fill.

The one legal way to bring in seasonal foreign workers is a program known as H-2A, which many farmers complain is overly complex and costly. While use of the program has steadily increased over the past decade, it still accounts for only about 10 percent of the estimated 1.3 million farm workers in the country, according to government data.

But labor advocates have blasted the H-2A guest worker visa program as a license for employers to abuse workers' rights due to the transient nature of guest worker residency, which lacks a pathway to citizenship and doesn't allow for guest workers to organize into trade unions.

teleSUR takes a look at a day in the fields of some workers with H-2A visas in California.