International container lines, except under very limited circumstances, will not be able to reload cargo unloaded at a West Coast port that is destined for another port on the coast, according to U.S. Customs.

After the lock-out of West Coast dockworkers was suspended last week, several container lines chose to offload the full volume of a ship's U.S.-bound cargo at the vessel's first U.S. port of call instead of steaming to a second port where it may face another lengthy delay for berth space.

That resulted in cargo being stranded at a port far from its final destination, requiring it to be shipped by vessel, train or truck. There had been some confusion whether a foreign-flag carrier could pick up cargo it deposited at one port, say Seattle, and carry it down the coast to Los Angeles. Customs said on Tuesday that such moves would not be allowed due to restrictions in the Jones Act, which requires that cargo shipped between U.S. ports be moved on vessels built, owned and crewed by Americans. "The Jones Act can only be waived in very rare circumstances," said a Customs spokesman.

The exception: cargo that a carrier offloaded immediately before the lock-out was imposed on Sept. 29. This could be picked up by the same carrier, but that would probably amount to relatively little cargo.

"Cargo caught in the moment on the pier will be allowed by exception to be picked up by another ship of the came carrier," the spokesman said, but not cargo initially dropped off by a ship that had been sitting at anchor.

The decision by Customs not to allow cargo destined for another U.S. port to be reloaded will exacerbate the situation faced by carriers and shippers. It means that cargo is essentially stranded and most be moved, possibly at the shipper's expense, to its final destination because of the force majeure declarations by many carriers.