Federal immigration officials yesterday raided the construction site for the new federal courthouse in downtown Richmond and arrested 33 immigrant workers from six Central and South American countries.

Immigration and Customs Enforcement agents, assisted by Virginia State Police, rounded up 29 men and four women working at the site who allegedly were living here illegally.

They each were charged with administrative immigration violations and are being detained for further processing, said Ernestine Fobbs, a spokeswoman for ICE in Washington.

The workers' native countries included Mexico, Honduras, Guatemala, El Salvador, Nicaragua and Peru, Fobbs said.

Fobbs said the investigation is ongoing.

State police did not participate directly in the raid. Four state troopers were on site to assist traffic flow, spokesman Sgt. Tom Cunningham said.

Fobbs said the workers could face additional charges if authorities determine they violated any laws.

"It could be for re-entering the country after deportation, it could be identity fraud, anything like that," Fobbs said.

Criminal charges against the workers would be referred to the U.S. attorney's office for the Eastern District of Virginia for prosecution, she said.

Fobbs declined to say what sparked the investigation and raid.

"I know the workplace is cooperating . . . with us in this investigation," she said of courthouse contractors.

The builder for the project is Tompkins Builders Inc., based in Washington, which does privateand public-sector construction. Other projects handled by Tompkins include the Gaylord National Resort and Convention Center just outside Washington and the National World War II Memorial.

James Tolbert, the company's vice president for business development and marketing, referred questions to Turner Construction Co., Tompkins' parent company.

"We are cooperating with authorities on an investigation of subcontractors on the Richmond federal courthouse job site," said Chris McFadden, a Turner spokesman. "The investigation does not involve any employees of Tompkins Builders or its parent company, Turner Construction Co."

McFadden said the number of subcontractors at the site changes periodically, depending on the type of work being done, and that he couldn't provide how many currently were under contract or their names. He said he didn't know which contractor or contractors employed the arrested workers.

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Several workers who witnessed yesterday's raid were willing to talk about what happened but not give their names out of fear of being fired.

They said the day began as usual but that at one point, workers were told to leave their equipment outside and enter the building for a safety meeting.

When they went to the second floor, they saw a number of immigration agents in hard hats waiting for them, the workers said, and everyone was asked to provide a legal ID.

Those with legal IDs were given red plastic bracelets and told to wear them all day. Two workers said they saw agents load four vans with men and one van with women.

Carl Tobias, a professor at the University of Richmond law school, said the case could prove similar to the federal prosecution of Michael Vick on dogfighting charges.

"This use of prosecutorial power really sends a strong message," Tobias said. "Other construction operations -- federal or not -- will sit up and take note when they see even the federal courthouse doesn't give you any immunity."

Coincidentally, he said, if the courthouse opens soon enough, it's possible some of those charged could be tried in the building they helped construct.

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The courthouse building at Seventh and Broad streets is in the final stages of construction and is expected to open this summer.

The $104 million structure, developed by the federal General Services Administration, will replace the federal court building at 10th and Main streets, parts of which date to before the Civil War.

Yesterday's raid was the second major immigration crackdown in the Richmond area in two years. In April 2006, immigration agents arrested 21 workers at the IFCO Systems of North America plant in eastern Henrico County.

Contact Mark Bowes at (804) 649-6450 or mbowes@timesdispatch.com.

Staff writers Frank Green and Linda Dunham contributed to this report.