Meanwhile, airport police department unions have complained about TSA "mission creep."

Mission creep "threatens the security of the airport," representatives of the American Alliance of Airport Police Officers wrote in a letter to Pistole in September 2012.

"TSA has expanded the scope of their authority beyond screening areas to more traditional 'police' work without clear lines of delineation with airport police, jeopardizing public safety, contributing to a break in chain-of-command, and delaying timely law enforcement responses," the group wrote.

"TSA agents are attempting to investigate and/or correct (security) breaches," the letter said, endangering the public, delaying police involvement and causing travel disruptions.

TSA employees should be restricted to conducting passenger and bag screening, the letter said.