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.