Labor negotiations between port clerks and shipping companies in southern California have come to a standstill, with a top union official warning that workers are prepared to walk off the job at any moment.

Attorney Steve Berry, the lead negotiator on behalf of 14 shipping companies and terminal operators who hired the clerks, said both sides were at an impasse.

"Each side has moved as far as they feel they can go at this point and can't go any further," he said.

The news comes hours after the two sides were expected to resume talks designed to dispel the threat of a work stoppage at the US's largest seaport area. So far, however, work on the waterfront in Long Beach-Los Angeles is reported to have continued as normal.

"We hope they wouldn't walkout. We've given a very generous wage and benefit package totalling more than 14 per cent over four years. We would provide the employees pay over US$80,000 per year and another $40,000 in benefits on top of that. We think it will be very unfortunate to shut down the harbor with that on the table," said Mr. Berry in a radio interview with KNX 1070 News.

On top of this package, workers would be given $3.4 million to establish a trust fund and a $40 per hour wage over two years. "There comes a point when you just can't give away more and we're at that point" he added.

Earlier, John Fageaux, president of the Local 63 Office Clerical Unit of the International Longshore and Warehouse Union (ILWU), said to the radio station workers were ready to strike.

"Talks are over (with the owners) as we've gone as far as we can and we've done everything we can do," Mr. Fageaux said. "The next step is we're going to get together with our group and determine when and where picket signs are going to go up."

The two sides have been bargaining for a new contract since May. Workers authorised their leaders to call a strike on the eve of their July 1 contract expiration, but have continued negotiations since that time.

To avoid a strike now, the union leader said the employers need to come to the union and address workers' concerns.

"I think we are relatively close, but there are a couple of key issues that apparently the employers aren't willing to budge on and we couldn't close that gap," said Mr Fageaux. "We made concessions that we thought would get us closer to an agreement. We listened to what the employers said, to their concerns, but apparently it was not enough for them."

More than 7,000 ILWU longshoremen who work in Long Beach and Los Angeles have agreed to honour picket lines put up by clerical workers, a move that would effectively lead to the port's closure, although administrative operations would continue. Other workers, including more than 650 machinists who work on the docks, have also pledged to honor picket lines.