WASHINGTON — Vowing to stop machines from taking their jobs, 45,000 U.S. longshoremen are threatening to go on a strike that would shut down ports on the East and Gulf coasts and could damage the American economy just as President-elect Donald Trump returns to the White House.

If the standoff sounds familiar, it’s because the same dockworkers — members of the International Longshoremen’s Association — staged a three-day walkout last fall. In October, they suspended the strike until Jan. 15 after reaching a tentative agreement with ports and shipping companies for a 62% pay raise over six years. But union members must approve a final contract before receiving the higher wages.

That’s where things get complicated.

Negotiations were set to resume Tuesday between the ILA and the U.S. Maritime Alliance, which represents ports and shippers. The sticking point is a familiar one at America’s ports: machines replacing human labor, specifically semi-automated cranes operated by software or employees working remotely to guide containers onto trucks or trains. Conventional cranes have a human at the controls.

The union and its president, Harold Daggett, are against allowing additional automation at East and Gulf coast ports. They argue that the machines aren’t any more efficient than human labor.

“This isn’t about meeting operational needs,” Daggett’s son Dennis Daggett, the union’s executive vice president, wrote last month. “It’s about replacing workers under the guise of progress while maximizing corporate profits at the expense of good-paying, family-sustaining U.S. jobs.”

Port operators and shipping companies argue that U.S. ports are falling behind more automated ports, such as those in Rotterdam, Dubai and Singapore.

Trump has already weighed in for the union, posting on social media that additional automation of ports would hurt workers.

Ports on the East and Gulf coasts handle more than half of the nation’s traffic in shipping containers.