Negotiations to end a strike at the biggest cargo port complex in the United States continued Monday, as the dispute enters its second week.

Unionized clerical workers at the Los Angeles and Long Beach ports in California walked off the job last Tuesday, claiming that shippers who operate out of the twin ports want to outsource jobs overseas. The group that represents the shippers and terminal operators say they merely want the right to hire the people they need.

Los Angeles Mayor Antonio Villaraigosa is demanding the two sides bring in a mediator and work nonstop until the dispute is settled. The National Retail Federation is urging President Barack Obama to intervene, warning that a prolonged strike could harm the still-fragile U.S. economy.

The Los Angeles and Long Beach ports account for nearly 40 percent of all imports shipped to the U.S., averaging $1 billion a day.

The 800 clerical workers have been joined by about 10,000 unionized dockworkers who have refused to cross the picket lines to load and unload cargo. Hundreds of truck drivers who haul goods to and from the ports have also been idled by the dispute.

Ten of the twin ports' 14 container terminals are shut down, forcing shippers to transport their cargo to other ports in California and Mexico.

Unionized dockworkers, also known as longshoremen, were locked out for 10 days at several U.S. West Coast ports in 2002.