Six labor recruiters have been accused of luring 400 farm workers to Hawaii from Thailand and mistreating them in what the FBI said is the largest human trafficking case ever charged in U.S. history.

An indictment unsealed in Honolulu Thursday charges six people with conspiracy to commit human trafficking, including four employees of Global Horizons Manpower, Inc., a labor recruiting company. Two other recruiters based in Thailand were also charged in the case.

The indictment said Global Horizons brought 400 immigrants in 2004 from Thailand to the islands to work on farms in Hawaii and on the mainland. Prosecutors said the workers were lured with false promises of high-paying farm jobs but were exploited and forced into labor, often with little or no pay.

"It's a classic bait-and-switch what they were doing. They were telling the Thai workers one thing to lure them here. Then when they got here, their passports were taken away and they were held in forced servitude working in these farms," said FBI Special Agent Tom Simon. ?This is just appalling that this would occur.?

The immigrants worked at 13 to 14 farms on Oahu, Kauai, Maui and the Big Island, tending to coffee, fruits and vegetables. Their employers included Aloun Farms on Oahu as well as Maui Pineapple Farm, which is no longer in business. But the farm workers were also sent to 12 other states as far away as Florida, Ohio and Kentucky, the FBI said.

Global Horizons President Mordechai Orian -- one of six people indicted in this case -- claimed in an interview with KITV four years ago his company paid farm workers more than the minimum wage.

"Instead of $6.75 we are paying $9.99. We are providing free housing, free transportation," Orian said in 2006.

Federal prosecutors and the FBI said Global Horizons recruited Thai nationals, often getting them to mortgage their homes or farms in Thailand to pay the company anywhere from $9,000 to $21,000 to secure them jobs in the United States.

Even though they signed contracts guaranteeing certain wages, the immigrants were often paid much less or even forced to work on farms for free, the FBI said. And while they were told they would get work visas that allowed them to work legally in the United States for three years, sometimes the company only arranged for temporary visas that expired after a few weeks, according to attorneys for the laborers.

"In the old days, they used to keep slaves in place using chains and whips. These days, it's done through economic intimidation," Simon said.