Throughout the centuries, as ships have navigated oceans bearing all manner of freight, the companies that operate ports have pressed to limit what they spend on the people who load and unload cargo.

Dockworkers, for their part, have mobilized to pursue a greater share of the bounty through a familiar tactic: They have threatened to disrupt international commerce by going on strike.

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.

That, in a nutshell, is the history of labor relations on docks from Australia to Britain. And that dynamic is at the center of a contractual impasse now threatening to produce a debilitating strike starting Tuesday at ports on the East and Gulf Coasts of the United States.

Dock workers make no apologies for the wages they command — more than $200,000 a year in many cases, after factoring in overtime. They perform the dangerous and physically exhausting job of moving shipping containers on and off vessels, while keeping businesses and consumers stocked with goods.

History validates their assumption that their bosses are embracing automation in part as a way to reduce costs. The most obvious example is the advent of container shipping in the 1950s.

The new York Times