Congressional researchers and aviation experts say a 2007 law mandating the screening of all cargo on U.S. passenger planes could cost $3.75 billion over 10 years in implementation costs.

Democratic leaders pushed the measure requiring the screening of cargo by 2010 as a way to counter concerns terrorists may use cargo shipments in attacks on passenger planes.

Critics of the measure say it would cause a massive bottleneck because freight arrives at the airport in large aluminum crates, making individual screening cumbersome, USA Today said Wednesday.

TSA officials said the solution is requiring the 4,000 "airforwarders" who handle the vast majority of passenger cargo shipments to implement the screening process at their facilities rather than at the airport.

"We want the supply chain, before they assemble a load, to take individual boxes and screen them," TSA assistant administrator John Sammon said.

Sammon said TSA screeners will work with the airforwarders on the screening process and added the department is working on seals for screened boxes to indicate TSA approval.