"The World Customs Organisation and port authorities won't have the new equipment and staff needed by the law's July 1, 2012 deadline for 100 per cent screening," said Michel Danet, secretary general of the WCO, the Brussels-based organisation that represents 173 customs authorities worldwide.
"We are trying to come up with arguments to convince the US Congress to repeal or change the law," Mr Danet was quoted as saying in a report by The Associated Press.
It noted that the box screening legislation will affect the movement of 325 million containers from 600 container terminals worldwide each year.
According to a study commissioned by the WCO and released during a two-day conference on container security, the report concluded that the US law would cost millions to implement, cause massive logistical problems for ports and damage world trade.
"The world's top ports are unlikely to meet the 100 per cent scanning rate by 2012," said Frederic Carluer, a professor from Le Havre University in France, who carried out the WCO study.