A shortage of West Coast port workers has forced the busiest U.S. ocean trade gateway to largely shut on Friday, after months of strained labor negotiations between the union dock workers and their employers.

A substantial number of ports of Los Angeles and Long Beach workers, including operators needed to load and unload cargo, failed to show up on the job starting Thursday evening, according to the Pacific Maritime Association (PMA), which represents employers.

The PMA said the missing workers were a result of a coordinated action by the International Longshore and Warehouse Union (ILWU) to withhold labor as contract talks drag on.

"The action by the union has effectively shut down the ports of Los Angeles and Long Beach," the PMA said in a statement.

Instead, the ILWU said the slowdown was due to thousands of union workers attending a monthly membership meeting on Thursday evening and observing the Good Friday holiday the following day.

"Cargo operations are ongoing as longshore workers at the ports remain on the job," ILWU Local 13, which represents union members at both the Los Angeles and Long Beach ports, said in a statement.

Operators at the Port of Long Beach decided to temporarily close four of the seaport's six terminals when workers did not show up on Friday morning, port spokesman Lee Peterson said, adding that regular operations at the seaport were expected to resume on Saturday.

Port of Los Angeles officials were communicating with the ILWU and PMA, along with federal, state and local officials, to "support a return to normal operations," said the group, which is managed by a unit of the City of Los Angeles.

Union workers at the ports have been on the job without an employment contract since the previous agreement expired on July 1, 2022, and the labor dispute has forced major retailers to shift cargo to East and Gulf Coast ports to avoid disruptions.

The ILWU and PMA have recently said they reached a tentative agreement on key negotiation sticking points and were committed to resolving the contract matter expeditiously as the administration of President Joe Biden continued to meet with the groups to help facilitate a deal.

(Reporting by Laila Kearney in New York; editing by Diane Craft)