However, the Pacific Maritime Association said terminal yard, rail and gate operations at the ports, which handle nearly half of U.S. maritime trade and over 70 percent of imports from Asia, will go on at the discretion of terminal managers through Saturday and Sunday, the group said.

The announcement came as tensions mounted over negotiations on a new labor contract for 20,000 dockworkers, represented by the International Longshore and Warehouse Union, that have dragged on for nearly nine months.

“In light of ongoing union slowdowns up and down the coast which have brought the ports almost to a standstill, PMA member companies finally have concluded that they will no longer continue to pay workers premium pay for diminished productivity,” the association said in a brief statement.

It said vessel loading and unloading operations were scheduled to resume on Monday, while yard operations – moving unloaded cargo containers for truck and rail delivery to customers – would continue at terminal operators’ discretion.

The union, insisting the two sides were close to reaching a settlement, branded the shippers’ move as another act of public posturing that would distract from the talks.

News of the weekend suspension came two days after the PMA’s chief executive, James McKenna, warned that ports plagued by severe cargo congestion in recent months were nearing the point of complete gridlock.

The companies have repeatedly accused the union of orchestrating work slowdowns at the ports to gain leverage in contract negotiations that have dragged on for nine months

The union denies this and has faulted the carriers themselves for the congestion, citing numerous changes in shipping practices as contributing factors.

The union also has downplayed the magnitude of the congestion, suggesting that management was exaggerating a crisis as a late-hour negotiation ploy.

“Closing down the ports over the weekend is a crazy way to do business because it’s hurting customers and adding to the already serious congestion crisis that the industry has created,” union spokesman Craig Merrilees said. “We can’t afford to be distracted by gimmicks and games.”

The last time dockworkers’ contract negotiations 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 as he invoked the 1947 Taft-Hartley Act.

Then as now, the companies accused the unions of instigating work slowdowns, and the union blamed management.

The PMA has estimated that the 2002 lockout cost $15.6 billion in economic losses.