Confronted by the militancy of longshore unions, port operators have deployed automation, in part to limit their vulnerability to labor troubles. Not coincidentally, dockworkers tend to look suspiciously at robots and other forms of innovation, divining threats to their livelihoods.

Tens of thousands of US dockworkers plan to strike next week if there is no breakthrough on contract talks, just a month before November's closely contested presidential election.Negotiations on a new contract began in May but have stalled in recent weeks.

A strike could disrupt the delivery of billions of dollars’ worth of consumer goods during peak shipping season. About 60% of America’s containerised trade would be affected. The value of containerised imports at the 36 ports amounted to $588bn last year. A strike would shut five of the ten busiest ports in North America.

At least 25,000 dockworkers at East and Gulf Coast ports could walk off the job next week, impacting about half of the country's imports and possibly sending prices higher for consumers. Negotiations between the workers' union and the employers face a Tuesday deadline.