Ports on the East and Gulf Coasts could close next week if dockworkers and employers cannot overcome their big differences over the use of automated machines to move cargo.

The International Longshoremen’s Association, the union that represents dockworkers, and the United States Maritime Alliance, the employers’ negotiating group, on Tuesday resumed in-person talks aimed at forging a new labor contract.

After a short strike in October, the union and the alliance agreed on a 62 percent raise over six years for the longshoremen — and said they would try to work out other parts of the contract, including provisions governing automated technology, before Jan. 15.

If they don’t have a deal by that date, ports that account for three-fifths of U.S. container shipments could shut, harming businesses that rely on imports and exports and providing an early test for the new Trump administration.

“If there’s a strike, it will have a significant impact on the U.S. economy and the supply chain,” said Dennis Monts, chief operating officer of PayCargo, a freight payments company.

The union is resisting automation because it fears the loss of jobs at the ports. President-elect Donald J. Trump lent his support to the union’s position last month. “I’ve studied automation, and know just about everything there is to know about it,” he said on his website Truth Social. “The amount of money saved is nowhere near the distress, hurt, and harm it causes for American Workers, in this case, our Longshoremen.”