Fort Myers, Fla. - A federal grand jury in Fort Myers has indicted three men and one woman for harboring people who are in the United States illegally.

Prosecutors say the four threatened to beat workers they were using to pick produce in the Immokalee area.

The government says the Navarrete family held the workers as virtual captives, forcing them to live in vans and sheds. The grand jury indicted Cesar, Jose and Geovanni Navarrete, as well as their mother, Virginia.

Prosecutors say the Navarretes kept about a dozen undocumented workers on their property in Immokalee. The indictment claims, workers had to pay rent and buy their meals from the family.

Three workers called in the initial tip to the Collier Sheriff about two weeks ago. The workers claim, the Navarretes locked them in a U-Haul van, but they escaped.

"The working conditions these people were in, were horrible. They were locked in box trucks, crates and sheds," says Assistant U.S. Attorney Doug Molloy.

Federal agents, armed with search warrants, raided the Navarrete property last week, arresting the three brothers and their mother.

The criminal complaint quotes some workers as saying the Navarretes beat them and chained their hands to keep them from leaving and finding other jobs.

The government deported two of the defendants some time ago, but they came back to the U.S. illegally.

If convicted, each defendant could face up to 10 years in prison, for each person they harbored. Prosecutors are also looking into the possibility of stronger charges such as human trafficking.