IMPORT volume at the nation's major container ports is expected to increase 3.5 per cent in May as new labour contract talks start with west coast dockers, says the monthly Global Port Tracker report.

"We're expecting a lot of cargo to move through the ports this summer and we want to make sure there aren't any supply chain disruptions," said Jonathan Gold, vice president National Retail Federation (NRF).

"The sooner labour and management can agree on a new contract, the better it will be for everyone who relies on the west coast ports," said Mr Gold, whose organisation commissions the report.

Representatives of the Pacific Maritime Association and the International Longshore and Warehouse Union start talks next week to replace the current contract that expires June 30.

West coast ports handle more than two-thirds of US retail container cargo each year. The last major shutdown there occurred in the fall of 2002, closing ports for 10 days and creating a backlog to be cleared.

US ports followed by Port Tracker handled 1.3 million TEU in March, the latest month for which actual results are available. The number was up 5.1 per cent from February, traditionally the slowest month of the year and up 14.5 per cent from March 2013.

April was estimated at 1.38 million TEU, up 6.1 per cent from the same month last year. May is forecast at 1.44 million TEU, up 3.5 per cent from last year; June at 1.43 million TEU, up 5.6 per cent; July at 1.49 million TEU, up three per cent; August at 1.5 million TEU, up 0.8 per cent, and September at 1.44 million TEU, up 0.1 per cent. The first half of the year is expected to total 8.2 million TEU, up 5.1 per cent over last year.

The total for 2013 was 16.2 million TEU, up 2.3 per cent from 2012's 15.8 million TEU.

The import numbers come as NRF is forecasting 4.1 per cent sales growth in 2014. Cargo volume does not correlate directly with sales but is a barometer of retailers' expectations.

"Most economic fundamentals are pointing in the direction of continued, sustained recovery in consumer demand and import volumes," said Hackett Associates Founder Ben Hackett, the report's author. "This is turning out to be the longest period of growth for some time now."

Global Port Tracker, which is produced for NRF by the consulting firm Hackett Associates, covers the ports of Los Angeles/Long Beach, Oakland, Seattle, New York/New Jersey, Hampton Roads, Charleston, Savannah, Port Everglades, Miami and Houston.