Most screening would be done by the 12,000 companies that truck goods from manufacturing plants to airports. The companies, called freight forwarders, would screen packages with X-ray machines and explosive sensors in warehouses where they are packed into large containers that are driven to nearby airports, TSA assistant administrator John Sammon said. Manufacturers also would screen boxes in factories.

The goal is to move screening away from airport cargo facilities, which are too small to check all freight, Sammon said. There is no plan for the TSA to pay for screening equipment or screeners, which Congress has said could cost $3.75 billion over 10 years.