Despite growing opposition from airlines and industry unions to the U.S. Transportation Security Administration’s new policy allowing passengers to carry small knives on planes, the agency’s head today said he is not backing down.

“I have to make sure that TSA’s focus is on those things that are most destructive to the aircraft,” TSA administrator John Pistole told ABC News. “It is not pocket knives. It is those non-metallic improvised explosive devices, the bombs that are very small. They are concealable and they are well designed.”

The new TSA policy, which will go into effect on April 25, will permit folding knives that do not lock and that have blades 2.36 inches or less in length and are less than 1/2-inch wide. Novelty-sized and toy bats less than 24 inches long, billiard cues, ski poles, hockey sticks, lacrosse sticks and two golf clubs will also now be allowed in carry-on luggage.