By Lisa Baertlein

LOS ANGELES, Feb 16 (Reuters) - The executive in charge of the largest West Coast seaport on Thursday called on employers and unions to finalize their labor contract, as worries mount over marketshare losses to rival ports amid reports of on-and-off negotiations.

Companies that regularly sent ocean containers of furniture, footwear, appliances and auto parts to the West Coast have been rerouting some cargo to the East and Gulf Coasts to avoid potential disruptions from labor talks that are taking longer than usual to resolve.

Those cargo shifts accelerated an erosion of the Pacific ports' control of the vital Transpacific trade lane from 80% in 2002 to 56% currently, Port of Los Angeles Executive Director Gene Seroka said on Thursday.

"We need this collective bargaining agreement in place quickly ... We don't want to give anyone excuses," said Seroka, who added that major retailers such as Walmart are preparing to negotiate their own agreements with container ship operators like Maersk and MSC that will help determine cargo flows.

More than 22,000 dockworkers at West Coast ports stretching from California to Washington State have been working without a contract since the previous one expired on July 1. The Pacific Maritime Association (PMA), which represents employers, and the International Longshore and Warehouse Union (ILWU) started talks in May.

In an email on Thursday, the ILWU said the parties are continuing to negotiate and that both sides agreed not to discuss talks in the media. The PMA did not respond to a request for comment.

On Feb. 10, the Journal of Commerce, a shipping industry publication, reported that stalled talks had resumed after negotiators for the union and employers put aside a pending dispute between ILWU and another union at a port terminal in Seattle.

Meanwhile, the top East Coast ports last year took the lead in U.S. container imports, handling 47.1% of that cargo versus 45.4% for the top West Coast ports, according to Hackett Associates, which produces the National Retail Federation's Global Port Tracker report.

In 2021, those West Coast ports processed 48.8% of imports, versus 44.9% for the East Coast, the firm said. (Reporting by Lisa Baertlein in Los Angeles; Editing by Bill Berkrot)