Striking workers shut down the largest terminal at the Port of Los Angeles for a second day Wednesday, and the job action later widened to close three terminals at the Port of Long Beach, threatening to paralyze the nation's busiest port complex.

About 70 clerical workers struck the APM Terminals operations on Pier 400 at Port of Los Angeles on Tuesday, raising the ante in a 2½-year-old contract battle over union claims that management has been outsourcing well-paid jobs out of state and overseas.

Only a handful of workers were picketing early Wednesday but dockworkers were honoring the walkout and the terminal remained closed, although only two cargo ships were affected, LA port spokesman Phillip Sanfield said.

"It's not crippling the port by any means. We've got eight other container terminals up and running," he said.

The port is not operating at its peak because shipment of Christmas goods ended several weeks ago.

"The holiday goods are either already in the stores or in warehouses," Sanfield said.

Port of Long Beach officials said Wednesday afternoon that a labor action there had shuttered operations at three of six container terminals.

About a quarter of a billion dollars in goods travel through the three terminals every day, Long Beach port spokesman Art Wong said.

Like Los Angeles, Wong said the Long Beach port's longshoremen were honoring the clerical workers' strike, and didn't cross picket lines to work.

Los Angeles and Long Beach together have the nation's busiest port complex. The twin harbors handled $273 billion worth of cargo last year.

The strikers are from the Office Clerical Unit of the International Longshore and Warehouse Union's Local 63. Their contracts with 14 companies who operate most of the terminals at the twin ports expired in June 2010.

Years of contract renewal negotiations ended with talks breaking off on Monday, leading to the walkout.

An arbitrator ruled Tuesday night that the union was negotiating in bad faith with shippers and the strike was invalid. However, the order was ignored. A second arbitrator also was expected to rule within two days on whether to uphold that order.

Clerical workers held brief strikes in 2010 and 2011 that ended after arbitrators ruled them improper.

For now, however, "they're on strike and picket lines are being respected," said Craig Merrilees, an ILWU spokesman in San Francisco.

The union risks a "dangerous escalation" if they continue to ignore the order, said Stephen Berry, lead negotiator for the Los Angeles/Long Beach Harbor Employers Association, which represented the 14 terminal operators in contract talks.

"It could lead to a spread of the job actions beyond just one terminal" and that, in turn, could prompt shippers to lock out employees, Berry said.

Still, it was unlikely that either side would want a repeat of a bitter 10-day lockout at a number of West Coast ports in 2002 that caused an estimated $15 billion in losses.

At issue is the union's contention that terminal operators have outsourced jobs to lower-paid paperwork pushers in the U.S. and places such as Costa Rica, India and Taiwan. A union release contended that 51 clerical jobs have been lost in the past five years.

Thanks to computer technology, shippers can easily "push buttons and maybe even get tax breaks" by moving work to other regions, Merrilees said.

Companies have refused to acknowledge there is an outsourcing issue, Merrilees said.

The negotiating group for the shippers denied that any local union clerical jobs were outsourced and said in a statement that the 51 workers had quit, died or retired with full benefits in the past three years.

Their positions weren't filled because there was no "business need," said a statement from the Los Angeles/Long Beach Harbor Employers Association.

In addition, the companies have offered to guarantee current union clerical workers their jobs for life, Berry said.

He claimed that the union wants contract language to permit "featherbedding" — the practice of requiring employers to call in temporary employees and hire new permanent employees even when there is no work to perform.