The group representing employers at West Coast ports prevented dockworkers from unloading ships Monday in order to clear out cargo containers from congested terminal yards.

The move, which prevented longshore workers from moving goods off ships still stranded in the water at the ports of Long Beach and Los Angeles, quickly attracted criticism from Rep. Janice Hahn, D-San Pedro, who urged the Pacific Maritime Association to reconsider its decision.

Nine container ships remained at sea Monday, waiting to be unloaded, according to the Marine Exchange of Southern California.

“At a time when cargo ships remain anchored, unable to dock because of a backlog at our West Coast ports, clearly there is much work to be done,” Hahn said. “Our dockworkers are ready to do it. Unfortunately, it has come to my attention that they are not being given the opportunity to work on unloading these ships this Monday. This move by PMA stands only to worsen the container backlog and hurt the small businesses across the country that depend on these imports.”

PMA spokesman Steve Getzug said that vessel operations during the day were suspended at West Coast ports Monday to focus on clearing containers from congested port terminals. Dayside vessel operations will resume today, he said.

PMA blames the International Longshore and Warehouse Union, the group representing 20,000 West Coast dockworkers at 29 ports, for not sending enough skilled crane operators to move containers, creating work slowdowns that have severely hampered terminal operations.

ILWU members have vehemently denied being the cause of work slowdowns and pointed to PMA’s decision to suspend ship unloading night shifts earlier this month and employers mismanagement for the gridlock.

Adan Ortega, spokesman for the ILWU Local 13, doesn’t buy PMA’s reason for shutting down unloading shifts to clear yards of containers. He said there is very little traffic inside the yards.

“What’s playing out on the ground is not the case,” he said.

Getzug said they were working to move cargo out, with 12 of 13 terminals ordering labor for their yards and gates Monday night.

The acrimony between PMA and ILWU continues to heighten as both sides engage in contract negotiations with a federal mediator Monday. Both sides have been in talks since May to hammer out a new contract to replace the one that expired in July.

Despite a tentative agreement on health benefits, talks have become heated in the last few months, exasperating congestion issues plaguing West Coast ports, especially at the ports of Los Angeles and Long Beach, the nation’s busiest seaport complex that both handle 40 percent of U.S. imports and employ hundreds of thousands of workers in Southern California.

The congestion — also due to the lack of available trailers to tow cargo containers and the increasing frequency of bigger ships coming to the ports — has resulted in shipment delays and has forced customers to reroute shipments to other ports and airports to bypass the West Coast.

Contact Karen Robes Meeks at 562-714-2088.