IMPORT volumes at major US ports are expected to go up 7.5 per cent in June as retailers bring in high quantities fearful of disruptions on the west coast after the dockers' labour contract expires, says Global Port Tracker.

"Retailers will keep the shelves stocked for the back-to-school and holiday seasons," said National Retail Federation (NRF) vice president Jonathan Gold.

The Pacific Maritime Association and the International Longshore and Warehouse Union began negotiations last month on a new contract to replace the agreement that expires June 30.

West coast ports handle more than two-thirds of US retail container cargo, including the bulk of cargo from Asia. The last major coast-wide shutdown occurred in 2002, closing ports for 10 days and creating a month-long backlog.

US ports followed by Global Port Tracker handled 1.43 million TEU in April, the latest month for which after-the-fact numbers are available. The number was up 9.9 per cent from March and 10.3 per cent from April 2013.

May was estimated at 1.47 million TEU, up 5.8 per cent from the same month last year, and June is forecast at 1.46 million TEU, up 7.5 per cent from last year.

Both are unusually high numbers not normally seen until later in the summer or fall, a sign that retailers have begun bringing imported merchandise into the country early because of the uncertainty.

July is forecast at an even-higher 1.51 million TEU, up 4.4 per cent from last year; August at 1.52 million TEU, up 1.9 per cent; September at 1.45 million TEU, up 0.8 per cent; and October at 1.48 million TEU, up 3.4 per cent.

The first half of the year is expected to total 8.3 million TEU, up 6.5 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.