LOS ANGELES — The container ships arrive here filled with appliances, toys, apparel, auto parts, computer components and untold other products from Asia, to head out to stores and factories across America.

But a simmering labor dispute between the longshoremen’s union and shipowners has brought crippling delays here and to other West Coast seaports. And the slowdown escalated this week as owners said they would suspend the unloading of container and other cargo ships on Thursday, Monday and the weekend because of what they called “a strike with pay.”

The move followed a similar two-day limit on work last weekend that angered many port workers. They saw it as a ploy to punish them and increase pressure to settle on a new labor contract after nine months of negotiations, which continue with the aid of a federal mediator.

It seems certain to worsen the congestion at the West Coast ports, which together handle half of the container traffic entering the United States, including at the vast Los Angeles-Long Beach complex here and at ports in Oakland, Seattle and Tacoma, Wash. Manufacturers and farmers who rely on timely and predictable trans-Pacific trade fear even more serious disruptions.