SEATTLE -- Longshoremen at the Ports of Seattle and Tacoma refused to work on Thursday as part of a union protest against U.S. military involvement in Iraq and Afghanistan. Fellow union members along the West Coast are taking part, brining cargo traffic to a halt.

An arbitrator on Wednesday ordered the union that represents dockworkers at West Coast ports to tell members they must report to work and not take the day off, but union leaders in Seattle said they have given their support to any of their 2,000 members who chose not to work.

Pacific Maritime Association spokesman Steve Getzug said thousands of workers at ports along the West Coast failed to report to work on Thursday.

Workers were expected to return for the start of the evening shift, he said.

"There's no work happening so that means there's no cargo being unloaded and certainly being loaded either," Getzug said.

Seattle dockworkers gathered at their union hall holding signs that read "No Peace - No Work."

Herald Ugles, president of International Longshore and Warehouse Union Local 19 in Seattle, said most of their members are taking part in the walkout, and only a handful of people showed up for work.

"We need to stop this war, bring out troops home, and let's rebuild America - not Iraq," he said, adding that the act should not be interpreted as a strike. "The members decided on their own to do this."

He said dockworkers would continue to move perishable shipments and emergency supplies.

Truck drivers were lined up at Terminal 18 on Elliot Bay as there were not enough longshoremen to handle the container offload operation as quickly as usual.

Officials at the Port of Tacoma said almost all of the dockworkers failed to report to work Thursday morning.

The walkout came despite a decision from an arbitrator on Wednesday ordering the International Longshore and Warehouse Union to tell members to show up for work.

Arbitrator John Kagel declared that a unilateral walkout by longshore workers would violate the union's labor contract.

The union stood by its members on Thursday, issuing a statement saying workers were exercising their First Amendment rights to protest the U.S. war in Iraq.

At the Port of Oakland, protesters walked picket lines to convince truckers to take part in the work action.

The truckers were not being blocked from entering the facilities.

Union spokesman Craig Merrilees said the union was complying with the contract but declined to specify whether it had taken steps to order members to report to work for the day shift Thursday, as the arbitrator ordered.

"The decision by members to take a day off work on May 1 to protest the war is their right under the U.S. Constitution and it's about time that citizens stood up to tell the truth about the need to end the war," he said.

Getzug accused the union of secretly encouraging members to go ahead with an illegal walkout.

"Staging a coordinated work action violates the waterfront labor contract and comes at a time when the union has pledged to not have any disruptions while a new contract is being negotiated," Getzug said. "Any disruption at the ports works against the interests of millions of Americans whose jobs are directly or indirectly tied to the movement of cargo."

The West Coast ports are the nation's principal gateway for cargo container traffic from the Far East.

J. Craig Shearman, a spokesman for the National Retail Federation, said shippers and exporters expected no significant, long-term disruptions from the walkout.

"This is something that happens every year," Shearman said. "Shippers and exporters know about it and plan around it, and we don't expect to see any significant disruptions from it."

Contract talks between the union and employers began in March. The current six-year contract expires July 1.

Merrilees stressed that plans by some members to skip work Thursday were not related to the contract talks.

"This is not a part of the negotiations, which have been moving in a generally positive direction," he said.

The contract covers some 25,000 longshore workers at 29 ports in California, Oregon and Washington.

In 2002, longshore workers across the West Coast were locked out for 10 days over a contract dispute. The shutdown cost the nation's economy an estimated $1 billion to $2 billion a day.