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Elaine Thompson, Associated Press
The Space Needle is seen just beyond a container ship anchored in Elliott Bay near downtown Sunday, Feb. 15, 2015, in Seattle. The waters off Los Angeles, Oakland and Washington state's Puget Sound have become parking lots for dozens of ships awaiting space at the docks. Employers are locking out dockworkers who man the cranes that lift cargo on and off ships, saying they have slowed work as a bargaining tactic, but the union denies that.

LOS ANGELES — The nation's top labor official is arriving in California in an attempt to resolve a damaging contract dispute between West Coast dockworkers and their employers.

U.S. Secretary of Labor Tom Perez is flying Monday to San Francisco, where negotiations between the dockworkers union and a maritime association of companies have come to a halt.

So, too, has processing of billions of dollars of cargo due to pass through 29 seaports from Southern California to Seattle. Over the holiday weekend, companies locked out workers who would normally load or unload ships.

Imports are stuck on massive vessels lined up outside the ports. Off Los Angeles and Long Beach, for example, 33 were waiting space at the docks.

Perez will attend negotiations Tuesday.