Panic shipping of goods into US Western ports by retailers and manufacturers who feared a possible dockworker strike this summer has instead resulted in a supply chain bottleneck at piers and terminals.

So much inventory is now stockpiled that warehouses are full and some retailers and importers are worsening the problem by hoarding the truck chassis used to tow intermodal containers away from the ships.

It seems the chassis are being used as "rolling warehouses" until a labour deal can be worked out.

Over the past two weeks the West Coast Waterfront Coalition, which includes Gap Inc, Target Corp and Wal-Mart Stores Inc, has been forced to ask shippers to return the chassis into the transportation logistical pipeline because of the bottlenecking problems.

Shipping companies can fine importers $100 for keeping the containers on the piers for more than five days and this, coupled with the financial burden of overbuilding the inventories, may ultimately be an extra cost that is passed to the consumer.

The International Longshore and Warehouse Union is locked in labour talks with the management group representing shipping companies, the Pacific Maritime Association (PMA). In the current debate the PMA wants to introduce labour-saving technology.