The last time contract talks led to a full shutdown of the West Coast ports was in 2002, when the companies imposed a lockout that was lifted 10 days later under a court order sought by President George W. Bush, invoking the 1947 Taft-Hartley Act.
The shipping industry has estimated the 2002 lockout caused $15.6 billion in economic losses. When it ended, some 200 freighters were waiting at anchor to be unloaded up and down the coast.
By comparison, 23 vessels were anchored awaiting berths on Monday outside Los Angeles and Long Beach, down from 31 on Sunday, port authorities said. Another 13 freighters were idled off the Puget Sound ports of Tacoma and Seattle.
Read MoreCongestion at West Coast ports is economic in part
Once a settlement is reached, it will take six to eight weeks to clear out the immediate backlog at the ports of Los Angeles and Long Beach—the nation's two busiest container cargo hubs—and possibly a few months more to restore freight traffic to normal, port representatives said.
The National Association of Manufacturers and the National Retail Federation have projected that a new 10-day port shutdown could cost the U.S. economy at least $2 billion a day. Both groups renewed their calls on Monday for the administration to ratchet up pressure for a settlement.
"If the administration can impart a message of urgency, that would certainly be helpful," said Robyn Boerstling, transportation director for the manufacturers group.
She said a number of manufacturers had reported that uncertainty surrounding the ports dispute had led some Asian buyers to cancel U.S. factory orders.
Industry executives say many retailers were already rerouting some seagoing shipments through the Eastern seaboard, the Gulf Coast, Mexico and Canada, as well as via air freight, changes that could add billions of dollars in costs to the supply chain.