Major U.S. ports will remain closed until wage demands are met, said the union leader representing striking longshoremen.

Harold Daggett, president of the International Longshoremen's Association (ILA), made the vow on a picket line in New Jersey on Tuesday as tens of thousands of longshoremen on the East and Gulf Coasts walked off picket lines to demand better labor contracts.

“We will fight for this and win, otherwise this port will never be reopened,” he said. “I’m not playing any games here.”

Companies are preparing for the possibility of an extended port closure that could devastating global trade and the U.S. economy.

President Joe Biden has so far rejected calls from some of the country's largest business groups to reopen ports under federal authority for 80 days to provide a cooling-off period for further negotiations.

“It’s only fair that workers who put themselves at risk to keep ports open during the pandemic should also see a significant increase in their wages,” Biden said.

“Now is not the time for shipping companies to refuse to negotiate a fair wage for these essential workers while reaping record profits.”

The strike, the first for the ILA since 1977, has brought container traffic to a halt at 14 of the country's busiest ports, including New York, Georgia and Texas.

Experts estimate the ports handle more than a third of U.S. imports and exports. Disruptions could result in delays in the delivery of goods for businesses and consumers.

The president said that in the event of possible shortages, officials would watch for signs of an unwarranted price increase.

Talks over a new agreement had been stalled for months before the strike, but the United States Maritime Alliance (USMX), which represents shipping companies and port associations, said the two sides had begun exchanging proposals again.

Under the 2018 contract, which expired Monday, port workers received a base hourly wage of $20 to $39 and other benefits, including royalties related to container traffic.

The latest offer would include a nearly 50% salary increase, tripling company contributions to retirement plans and improving health care, among other things. It also said the union had been asked to agree to an extension of the current agreement to allow for negotiations.

However, the ILA's Mr Daggett said there had been “nothing” so far to persuade the union and companies to end the strike.

He said he was willing to keep the ports closed until companies agreed to increase hourly wages by $5 for each year of the contract. The union, which has about 47,000 active members, according to federal records, is also seeking protection from automation.

“I will fight for this because these greedy companies are making billions of dollars and they don’t want to share it,” he said. “I want my members to be taken care of for the rest of their lives and that’s why we’re out here.”

If the shutdown continues for a longer period of time, it is expected to result in higher prices and shortages in the United States, with delivery delays and other impacts reverberating around the world.

“We are now seeing ships anchoring outside the ports and waiting to see what will happen,” said Anne-Sophie Fribourg, vice president of shipping company Zencargo, which organizes shipments for exporters and importers.

“The disruption will be massive if the strike continues,” she said.

There are already 100,000 containers waiting to be unloaded in the New York metropolitan area, with another 35 ships expected this week, the Port Authority of New York and New Jersey said.

Danny Reynolds, the owner of Stephenson's, a 93-year-old clothing store in Elkhart, Indiana, said he paid extra before the strike to expedite shipping of sweaters and coats into the country.

But about 25% of his inventory hasn't arrived yet and he's keeping his fingers crossed that it's been unloaded. He said he's most worried about potential delivery dates for custom-made wedding dresses for November and December weddings.

“We worry when we have custom orders for people's wedding anniversaries who might be trapped on a ship that can't reach us. That’s hard to explain to a potential bride,” he said.

About 75% of its goods move through ports on the East Coast, he added. He said that while he expected his company to be operational by the end of the year, he feared the far-reaching impact.

“I think the consequences for the economy could be devastating if this continues,” he suggested, adding that he wanted presidential intervention.

“I think, quite frankly, it’s no longer time for the Biden administration to sit down with them and see what can’t be done to make things right.”