A federal grand jury indicted 44 people Tuesday for allegedly using fake green cards and other false identification to work as contract employees at the Air Force Academy (search).

The workers included construction workers, landscapers and janitors hired by civilian contractors, said Jeff Dorschner, spokesman for the U.S. attorney's office. Twenty-seven people were arrested.

The workers, apparently all from Latin America, were caught as part of increased security at the academy after the Sept. 11 attacks. Previously, contract employers had been responsible for verifying the credentials of employees.

The 27 arrested held fraudulent green cards and counterfeit Social Security cards. They could face charges of misuse of a Social Security number (search), making a false statement and misuse of an identification card. If convicted of all three charges, the maximum sentence is nine years.

Federal agents have conducted more than 25 raids across the nation since the terrorist attacks, looking for illegal workers at secure federal installations and airports. Dozens have been charged.

There was no word of similar raids at the nation's other two military academies, at West Point, N.Y., and Annapolis, Md. Calls to U.S. attorneys near the two academies were not immediately returned.

The Air Force Academy outside Colorado Springs was among the first military installations in the state to set up a system using federal, military and civilian law enforcement personnel to check employee records, Dorschner said. Similar arrangements are being made elsewhere.

"We're pleased that Academy Security Forces were instrumental in facilitating today's law enforcement operation," said Col. John Miller, the academy's 10th Air Base Wing Commander.

Structures critical to U.S. security cannot be considered secure until the records of all workers are verified, U.S. Attorney John Suthers said. He said the academy should be applauded for tracking down the illegal workers.

"This nation simply cannot afford security vulnerabilities to exist in our critical infrastructure," added James Chaparro, a special agent with the Bureau of Immigration and Customs Enforcement.