AURORA, Colo. -- At least 122 illegal immigrants are on their way back to Mexico after a group of construction workers were rounded up by agents of Immigration and Customs Enforcement early Wednesday morning as part of a worksite enforcement operation.

About 40 federal agents interviewed workers, checking on their legal status. The illegal immigrants were working on a government contract at a construction site that's about a quarter-mile from the satellite monitoring systems on base.

The two main contractors on the base are Investment Builders Inc. and Hunt Building Company. In 2004, both El Paso, Texas, companies formed Buckley Family Housing LLC, which was awarded the $74.7 million contract to build and maintain 351 housing units at Buckley AFB.

It's not known if the men worked for the larger company or the other subcontractors involved in the project. Nevertheless, the contractors who hired these workers are in violation of a federal contract that requires any company working on a government project to employ only legal workers, ICE officials said.

"Hunt Building Company takes every precaution to ensure that its hiring practices are fully compliant with all applicable local, state, and federal laws," said Stephanie Sierra, Hunt Building Company's spokeswoman. "We require that all Hunt Building employees are within the boundaries of legal employment. It is our understanding that a single Hunt Building Company employee was detained by authorities for questioning. Our records show that the employee has all required documentation, including an I-9, Social Security number, and proper identification. Other workers on the project who may have been detained for questioning are not employees of Hunt Building Company."

The project had been under surveillance for the past two months. Federal authorities were concerned because there was no standard security for entering and exiting the base at that new construction location, and that was a security risk.

"The concern was (that) the construction was directly adjacent to Buckley Air Force Base, only separated by a chain link fence," said ICE agent Jeff Copp.

The national security concern centered on the site's location that is less than a quarter of a mile from Buckley's critical communication satellites.

"Having a construction site with workers who are unidentified and you don't know who they are, caused some concern," said Copp. "That's when we took action and moved it to the top of our priority list."

Officials said the raid started at 6 a.m. and lasted until 7:30 a.m. Nobody tried to run and the operation went without a hitch, 7NEWS reported.

The workers were loaded onto buses and vans and taken to a processing facility on the base where they are being detained and questioned by ICE agents. Those who were unable to prove they are legal in the country are being deported to their native countries, officials said.

During the operation, ICE agents were backed up by officers from the Aurora Police Department and Air Force investigators.

'I was shocked. I couldn't believe it. I've never seen anything like it before," said construction supervisor Tim Clark.

Clark watched as federal agents moved in on the construction site.

"It was just pandemonium for an hour or two," said Clark. "There was just nothing but people getting arrested. Maybe 30 people made it through. Everybody else got shipped out of here."

The federal agents must now determine who is responsible for allowing illegal immigrants to work at the site.

"What are you supposed to do if they have a Social Security number and an ID? Are we supposed to run them to see if they are fake or are they?" said Clark.

The workers were building 350 houses all part of a $75 million contract.

Federal agents said criminal charges could be filed.