And on Monday, Rep. Bennie Thompson of Mississippi said the decision appeared to have been made "in a vacuum" and will impact millions of passengers.
Thompson is the senior Democrat on the panel that will hear Pistole's testimony later this week.
Others opposing the change include the Flight Attendants Union Coalition, representing nearly 90,000 flight attendants, and the Coalition of Airline Pilots Associations (CAPA), which represents 22,000 airline pilots.
"We believe the threat is still real and the removal of any layer of security will put crewmembers and the flying public unnecessarily in harm's way," CAPA President Mike Karn said.
In addition to the small knives, the TSA will allow passengers to carry two golf clubs, toy bats or other sports sticks -- such as ski poles, hockey sticks, lacrosse sticks and pool cues -- aboard in carry-on luggage.
Pistole said in a three-month period last year, the TSA seized 47 small knives from passengers at Los Angeles International Airport alone. But the knives presented little threat to the plane, he said.
"Our greatest concern, the greatest risk, is non-metalic IEDs, whether that's explosive, whether that's (an) electronic initiator or a chemical initiator, whatever that may be. That's what I want I security officers to focus on," he said.