Millions of dollars worth of cargo has been left stranded outside ports on the West Coast of America after the second lock-out in two days by the Pacific Maritime Association (PMA).

The PMA represents shipping lines and sea terminal operators.

It is accusing dock workers, largely represented by the International Longshore and Warehouse Union (ILWU), of deliberately working too slowly as part of a long-running dispute over the terms of a new contract.

The White House has said it is keeping a close eye on the dispute.

Stalemate

More than 10,000 port workers have been without a contract since the last one expired on 1 July.

But the PMA and ILWU are at loggerheads over the pension and benefit packages associated with the new contracts.

The American public is going to pay for it this Christmas

The National Labor Movement

Another stumbling block is the PMA's plan to introduce new technology on the docks.

Port operators say the new machinery is essential to remain competitive, while union officials are concerned that the new equipment could cost workers their jobs.

The PMA has now said it will now bar workers from the docks across the West Coast until the union agrees to extend the lapsed contract while a new agreement is discussed.

Costly protest

While the two sides maintain their dispute, economists have warned that it could cause serious disruption to the US economy, particularly with the increase in shipments for Christmas.

The PMA has estimated that each day the ports are closed costs the US economy as much as $1bn (�637m) in Asian imports.

Miguel Contreras, a spokesman for the National Labor Movement said: "The American public is going to pay for it this Christmas."

The White House has said it is "monitoring it (the dispute) carefully", and could intervene if the work stoppage continues.

Both sides in the dispute were scheduled to resume a new round of talks in San Francisco on Monday afternoon.