Striking dockworkers picketed Tuesday morning at the shut-down road leading to the Conley Container Terminal in South Boston.

Some held signs reading “machines don’t feed families: support all workers” and “profit over people in unacceptable” in protest of a move toward more automation in the industry.

The Boston dockworkers are among thousands who went on strike at ports from Maine to Texas after their contract expired at midnight. Estimates say the strike at the 14 ports could cost $4.5 billion a day. But experts told GBH News that the local impact on Massachusetts is not yet clear, and will depend on how long the strike drags on.

“We’re really just looking to have our fair contract from the [United States Maritime Alliance] and we’re fighting automation, because automation will replace workers’ jobs,” said Bernie O’Donnell, international vice president of the International Longshoremen’s Association.

“We’re going to be here as long as it takes,” O’Donnell said. “We’re going to be here 24/7 on the picket line until we get a fair contract.”

In a written statement just before the contract expired, the United States Maritime Alliance said they made an offer to “increase wages by nearly 50 percent, triple employer contributions to employee retirement plans, strengthen our health care options, and retain the current language around automation and semi-automation.”

A spokesperson for Massport said in a written statement that Conley Container Terminal is closed until further notice. The statement says the port plays “a pivotal role in the economy of Massachusetts supporting 66,000 jobs and generating more than $8 billion annually,” and that truck turn times in Boston average less than 30 minutes.

“This helps keeps costs lower for customers and makes the Commonwealth attractive to new business,” the statement read.“ Boston was America’s first port, and more than 400 years later we are honored to keep that tradition alive.”

Boston’s port sees much less activity than it did in its heyday, said James Zagorsky, an economist at the Boston University Questrom School of Business. He said the impact here won’t be as significant as larger ports, like New York City, Savannah or Baltimore.

“If you’re looking at the logistics, the Port of Boston ranks 25th among the U.S. ports,” Zagorsky said. “We’re no longer huge.”

These days, Zagorsky said, the port of Boston is important for bringing in heavy items that are not cost-effective to ship by rail or trucking, like cars, tires and refrigerators.

”The second thing is lower value items that don’t have to be any place immediately,“ Zagorsky said. ”Last year, about 5 million pairs of shoes, sandals and other footwear came into the port.“

Some ships may be able to get around the strike by arriving at ports in Canada, Zagorsky said.

”There’s two particular ports, the Saint John and Montreal, they can offload there and then drive things over the border, over into Maine or over into New Hampshire and Vermont and bring things down from there,“ he said.

It’s not yet clear what the impact will be on imported cars, said Robert Okonowski, executive vice president and general counsel for the Massachusetts State Auto Dealers Association.

”We really need to wait and see how this plays out in terms of the length of time and what products we may be looking at that are being backed up in the in the delivery chain, the distribution chain,“ Okonowski said. ”In the medium to long term, if dealerships are not being replenished with vehicles and parts retailers are not being replenished with parts, it could make it very difficult on the retail side of things, if consumers are expecting certain products to be available.“

The impact on food imports may be felt sooner, but Brian Houghton, senior vice president of government affairs and communications at the Massachusetts Food Association, said it may be some time before that becomes clear, as well.

”If it’s drags on a week or two, concerns, I’m sure, are going to be raised,“ Houghton said. ”There could be shortages in produce, things that don’t have a long shelf life, a lot of perishable foods and such, because a lot of that is out of season right now and has to be shipped in.“

That kind of prolonged strike could impact retail stores across the region, said John Hurst, president of the Retailers Association of Massachusetts.

”This is a huge concern for the retail sector and their customers,“ Hurst said. ”And whether you’re a mom and pop store or you’re a national chain, we’re entering the all-important fourth quarter of the calendar year. And that’s the time that makes or breaks profitability for a lot of stores. And it’s when consumers are more likely to do those impulse buys and do the shopping for the holiday season for the loved ones. So the timing couldn’t be worse. You know, we’re hopeful this will be short because if this if this drags on for a long period of time, the economic impact just compounds.“

GBH’s Mary Blake contributed reporting for this story.