From the story:
In interviews with Salon, the former AT&T workers said that only government officials or AT&T employees with top-secret security clearance are admitted to the room, located inside AT&T's facility in Bridgeton. The room's tight security includes a biometric "mantrap" or highly sophisticated double door, secured with retinal and fingerprint scanners. The former workers say company supervisors told them that employees working inside the room were "monitoring network traffic" and that the room was being used by "a government agency."
The details provided by the two former workers about the Bridgeton room bear the distinctive earmarks of an operation run by the National Security Agency, according to two intelligence experts with extensive knowledge of the NSA and its operations. In addition to the room's high-tech security, those intelligence experts told Salon, the exhaustive vetting process AT&T workers were put through before being granted top-secret security clearance points to the NSA, an agency known as much for its intense secrecy as its technological sophistication.