More than 100 workers at Chicago's O'Hare International Airport have been found with fake security passes, officials have said.
Tighter airport security measures have been introduced since 9/11
Authorities said 110 of the badges issued to a contracting company did not match their owners.
A total of 23 illegal immigrants were arrested and accused of using the fake badges to work in secure areas.
The US has tried to introduce rigorous security measures at airports since the attacks of 11 September 2001.
Of those arrested, 21 are from Mexico and two from Guatemala, the Associated Press new agency reported.
The case concerns workers employed by Ideal Staffing Solutions, which contracted work for carriers including United Airlines, KLM and Qantas.
Applications for the 110 fake badges used social security numbers that did not exist or belonged to other people, some of them dead.
One worker is said to have told investigators he was asked to rummage through a box of about 20 airport security passes and pick one with a picture that looked like him.
The office of Cook County State's attorney has issued more than 100 arrest warrants in the case.
Since the 9/11 attacks, the US aviation department has implemented rigorous screening of everyone allowed access to secure areas, including fingerprinting, an FBI criminal check and a security threat assessment.