In 2014, the start of labour negotiations involving dockworkers across the coastlines of California, Oregon and Washington was followed by a months-long slowdown at container ports.

It could have been worse.

In 2002, for example, stalled talks led the Pacific Maritime Association (PMA) — the employers’ group — to lock out workers across the US west coast.

The next round of these often fraught labour negotiations is set to begin next month, with the two sides aiming to reach an agreement before the contract for 15,000 dockworkers at 29 ports from San Diego in Southern California to Bellingham in Washington state are set to expire.