Cargo at Los Angeles and Long Beach, by far the busiest ports in the nation, has been taking unusually long to clear the docks since the summer. Both sides agree a big cause of the congestion is a lack of truck chassis that carry containers off sprawling lots and into the flow of commerce.

Now add what employers term a work slowdown, and the twin ports are approaching "the brink of gridlock," the association said in a statement.

A spokesman for the union did not deny a slowdown, but he also blamed employers for the congestion.

Cargo flow is gummed up for several reasons that predate the recent labor issues, union spokesman Craig Merrilees said. There has been a shortage of not just truck chassis, but also drivers to move containers to distribution centers, an issue Merrilees attributed to poor wages and exploitative working conditions.

"The problems are industry caused, self-inflicted and serious," he said.

Past negotiations have seen work slowdowns. During contract negotiations in 2002, employers locked out longshoremen following slowdown allegations.

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