The exploitation of impoverished Thai farm workers by a Los Angeles-based labor contractor went on for longer than federal prosecutors had previously disclosed and involved more workers and more growers in more states, including Del Monte and Aloun Farms on Oahu and a macadamia nut farm on the Big Island, according to a federal indictment unsealed yesterday.

The indictment, an update to one returned last September, adds more charges of forced labor and related offenses against labor contractor Global Horizons Manpower Inc. owner Mordechai Yosef Orian and five alleged co-conspirators, officers in his company and recruiters in Thailand. The new indictment adds two more Global Horizons officers as defendants.

Aloun Farms owners Alec and Mike Sou are facing separate federal forced-labor charges for actions unrelated to Global Horizons.

Last September’s indictment said Orian, 45, an Israeli national, and his co-conspirators exploited about 400 Thai workers in forced-labor conditions from May 2004 to September 2005. It named only one property where the workers were allegedly confined and forced to work, the valley isle’s now-defunct Maui Pineapple Farm.

The new indictment alleges Mordechai and others exploited about 600 farmworkers from 2001 to August 2007, transporting them first from their native Thailand, then shuttling them between farms in Arizona, Hawaii, Mississippi, California, Utah and New York.

To transport the workers interisland and between states, the defendants gave back the workers their passports to board commercial airplanes and re-confiscated them when the workers reached their destinations, the indictment said.

The defendants later transported the workers by private aircraft, the indictment said. On two occasions in 2005, Orian transported workers to his home in Kona for a barbecue in lieu of paying them for their work, the indictment said.

The defendants targeted workers who earned just $1,000 a year in Thailand and promised them $2,000 per month for eight hours of work per day plus overtime, the indictment said. However, the defendants required the workers to pay upfront recruitment fees ranging from $9,500 to $26,500, using their land and homes as collateral.

When the workers complained about getting paid less than promised, getting paid late or sometimes not at all, the defendants threatened to — and in some cases did — send them back to Thailand with no opportunity to pay back their loans, the indictment said.

When the workers tried to flee, the defendants threatened them with physical harm, kept them under guard and in some instances locked them in their living quarters when they were not working, the indictment said.