MINNEAPOLIS (WCCO) — Authorities say they are investigating after the Minneapolis-St. Paul International Airport’s FAA building was delivered a letter “containing a suspicious material.”

The FBI says that four Federal Aviation Administration employees sought medical assistance as a precaution.

(credit: CBS)

The FAA building’s employees oversee aircraft certification, security, regulatory compliance and other airport functions.

Standard operations at MSP Airport were not affected, the FBI reported.

“Air traffic control functions are not located in this building and have not been affected,” read the FAA’s statement in response to the incident. “The FAA is investigating, and is cooperating with other investigating authorities, including the Department of Homeland Security.”