Immigrant workers from Mexico were allegedly locked in shipping containers after spending the day working to build luxury condos in the South Bay.

The United States Department of Labor said the workers were held against their will and forced to work for nothing. The incident is allegedly tied to the Silvery Towers being built in downtown San Jose.

On Thursday, critics and unions called the development the "Slavery Towers." The developer in response has shut down the project.

Union members angry at the news that at least 22 of their coworkers were actually victims of human trafficking. US Dept. of Labor officials said that after work, the men were locked in a shipping container.

Federal agents two weeks ago arrested the unlicensed sub-contractor who hired them. Video obtained by NBC Bay Area shows a related raid in Hayward.

Federal officials said the workers were never paid for helping build the Silvery Towers luxury condos.

"It's a dark day when workers are treated like dogs," said Will Smith, with IBEW Local 332.

The developer, Full Power Properties, paid the lost wages even though they were not obliged to do so. Those who have spoken to the workers said the sub-contractor threatened violence on them or their families in Mexico at the hands of drug cartels if they sounded the alarm.

Watchdog groups said those kinds of threats are not rare in Santa Clara County.

"We see that in a lot of our trafficking cases, where there's those kinds of threats of cartels," said Ruth Silver Taube, South Bay Coalition to End Human Trafficking.

In a statement, the developer said they fired the sub-contractor immediately when they heard the allegations last year. The developer was not fined for any wrongdoing.

A San Jose councilman who showed up Thursday said this is not the city's proudest moment.

"It is extremely embarrassing, not just devastating," San Jose Councilman Raul Peralez said. "It's embarrassing to have this happen under our watch."

Full Power Properties said Thursday was just a misplaced publicity stunt by the unions. NBC Bay Area was scheduled to speak with some of the workers who were allegedly victimized, but they are still fearful of what might happen to them or their families back home.