The US Chamber of Commerce is calling on President Joe Biden to intervene in a labor dispute involving US West Coast ports that has seen container ships face delays from labor-related disruptions.

“We urge you to appoint an independent mediator to help the parties reach a voluntary agreement,” Chamber President and Chief Executive Officer Suzanne Clark wrote in a letter to the president Friday, as talks between port employers and dockworkers approach a one-year mark without a contract.

“This step is necessary to avoid potentially billions of dollars in economic damage to the American economy before it occurs,” Clark added. “We urge your Administration to continue engaging directly with both parties and to consider additional steps that may be necessary in the event of a widespread work stoppage.”

Read more: LA Ports Prepare to Manage Ship Traffic as Labor Disrupts Cargo

Labor shortages at West Coast ports that began last Friday stretched into the week, making it the longest disruption related to contract talks since the White House intervened in 2015. A previous labor contract covering 22,000 dockworkers at 29 ports expired on July 1, 2022.

Operations at the Ports of Los Angeles, Long Beach, and Oakland have improved since labor actions began June 2, though the Ports of Seattle and Tacoma continue to see “targeted” slowdowns by the union, said the Pacific Maritime Association in a statement Friday.

Terminals at LA and Long Beach “have for now averted the domino effect” that would have backed up supply chains, said the PMA, which represents ocean carriers and terminal operators.

The International Longshore and Warehouse Union declined to comment.

Dozens of container ships scheduled in the next week for the twin ports of LA and Long Beach were affected by delays of a day or two, according to the Marine Exchange of Southern California.

There were concerns the delays can have broader fallout as ships that are off schedule can cause disruptions at other ports on their routes.

Clark warned of a crippling effect on the US economy.

“A serious work stoppage at the ports of Los Angeles and Long Beach would likely cost the U.S. economy nearly half a billion dollars a day – and a more widespread strike along the West Coast could cost approximately $1 billion per day,” Clark said in the letter.

The White House said this week that Biden respects the collective bargaining process and wants negotiations between port employers and workers to continue.

(Adds PMA statement on improved cargo operations in 5th, 6th paragraph)