Three US men have pleaded guilty to human trafficking charges related to a company that recruited farm workers from Thailand.

The U.S. Justice Department says between 2001 and 2007 the defendants brought some 600 Thai nationals to the United States under the federal agricultural guest worker program.

The indictment says the men forced the Thai nationals to work by taking their passports, threatening them with harm and repatriation, and forcing them to incur substantial debt secured by their homes and family land in Thailand.

The three men face maximum sentences of five years in prison.

Another man associated with the company was charged and convicted of recruitment fraud in Thailand and sentenced to four years in prison.