A massive strike by longshoremen at seaports on the US East and Gulf coasts is expected to wreak havoc on global supply chains and the economy, with US consumers likely to notice shortages of popular products if the work stoppage continues for long.

Workers at ports stretching from Maine to Texas went on strike early Tuesday over a dispute over wages and automation. The action, which is likely to have serious consequences for ships carrying billions of dollars in cargo, is the first by the International Longshoremen’s Association (ILA) union in almost half a century.

The ILA, which represents about 45,000 dockworkers, has made good on its threat to strike at 14 major ports after talks with the United States Maritime Alliance (USMX) employers’ group broke down ahead of a September 30 deadline.

“The key premise here is that duration increases impact,” Lisa DeNight, director of national industrial research at Newmark, told CNBC’s “The Exchange” on Monday.

“If this strike continues for a few days, the consequences will be quite short-lived, I would say. If this continues, it will have a huge impact on the entire global economy – and not just the US economy. The unpredictability of this problem really comes into play here and it has the magnitude to really throw a huge wrench into global supply chains,” she added.

DeNight said even a minor disruption lasting just a few days could have “very significant impacts on certain industries,” including pharmaceutical, automotive and manufacturing.

Ocean supply chains have already been hit hard this year by conflict in the Red Sea, a prolonged drought affecting the Panama Canal and the collapse of the Baltimore Bridge.

Still, Peter Sand, principal analyst at ocean freight rate information platform Xeneta, has said that with more than 40% of total “containerized goods” entering the U.S. through East and Gulf Coast ports, “the stakes couldn’t be higher.” “

Speaking to CNBC’s ‘Street Signs Europe’ on Tuesday, Sand said he expects the strike to last a week.

“We’re now seeing the dominoes falling in multiple phases. Initially, of course, the immediate impact is on the US East and Gulf Coasts, right?” said Sand.

There will then be a knock-on effect for ships currently queuing outside ports, he added, meaning their next trips to the US carrying new goods will be postponed.

“We will see disruption towards the end of October and early November as some ships leave Europe and the Mediterranean late,” Sand said.

The ships will be delayed leaving Asia in late December and early January – “which is actually when the next normal mini-peak in container shipping occurs in the run-up to Chinese New Year.”

“So it’s really a tight time with so many things at stake. You could say it’s a perfect storm, but it’s also a really good bargaining position for people who want a strike,” Sand said.

For U.S. consumers, he said the strikes could soon lead to shortages of perishable or temperature-controlled goods such as bananas and other fresh fruit.

Danish shipping giant Maersk has warned that recovery from just a one-week shutdown could take four to six weeks, “with significant backlogs and delays increasing every day.”

In an update published on Monday, Maersk said the disruption would likely lead to freight delays, higher costs and logistical challenges for companies dependent on ports on the US East Coast and the Gulf. A prolonged labor dispute, the company added, could exacerbate these disruptions.

However, not everyone is equally concerned about the broader economic consequences of the strikes at US ports.

Bradley Saunders, North American economist at Capital Economics, said in a research note published late last month that the strike action is unlikely to lead to any major economic disruption because – despite advance denials – US President Joe Biden has “little choice ” would have, but to intervene and invoke back-to-work legislation ahead of the November elections.

Biden has said he will not use existing labor law to force union workers back to work, which is within his powers under the Taft-Hartley Act.

The Taft-Hartley Act, passed in 1947, was a revision of U.S. law governing labor relations and union activities that granted a U.S. president the power to suspend a strike for an 80-day “cooling off” period in cases where “national health or security” is at risk.

“Frequent shocks to supply chains in recent years have made manufacturers more responsive to the risks of low inventory,” Saunders said on September 25.

“It is therefore likely that companies will have taken precautions in the event of a strike – not least because the possibility has been touted by the ILA for months,” he added.

— CNBC’s Lori Ann LaRocco contributed to this report.