President Donald Trump’s new secretary of commerce has vowed to tax foreign-­flagged ships making calls to U.S. ports.

As many Hawaii businesses are already weighing the potential impacts tariffs proposed by Trump could have on them, some are now bracing for even more potential economic consequences if foreign ships visiting the islands have to pay extra for pulling into our harbors — potentially passing those costs on to the consumer, or prompting the ships to avoid Hawaii altogether.

In a Thursday interview televised on Fox, newly confirmed Commerce Secretary Howard Lutnick said “Donald Trump has announced the External Revenue Service, and his goal is very simple: to abolish the Internal Revenue Service and let all the outsiders pay.”

“I’ll give you an example: cruise ships. You ever see a cruise ship with an American flag on the back? They have flags of Liberia or Panama. None of them pays taxes. Every supertanker — none of them pays taxes,” Lutnick said. “This is going to end under Donald Trump. Those taxes are going to be paid.”

According to Lloyd’s List, a publication that covers the international shipping industry, cruise line stocks plummeted just moments after Lutnick’s remarks. At their lowest on Thursday morning, the aggregate market capitalization of the four U.S.-listed cruise companies — Carnival, Royal Caribbean, Norwegian Cruise Line and Viking — was down $15.4 billion, or an average of 10%. The stocks gradually traded back as other investors saw an opportunity, but it offers a look into the uncertainty that oceangoing companies see in the American market.

Cruise ship passengers make up just 2% of Hawaii’s annual visitors, but foreign ships delivering oil and other goods commonly stop in the islands. Ships delivering fuel in particular have become central to how Hawaii’s economic, energy and transportation systems function — more than 80% of oil is imported from foreign sources.

“If he’s going to start imposing a surcharge or a tax on any foreign vessel that comes to America, in this case this would really affect our oil supplies, the cost of our energy,” said Mark Coleman of the Grassroot Institute of Hawaii, a libertarian­- leaning think tank.

In Hawaii two companies — Matson Inc. and the Pasha Group — largely dominate shipping between the islands and the mainland. They have maintained their regional dominance in part with the help of the 1920 Jones Act, which requires that trade between U.S. ports be limited to ships that are American-flagged, American-built and crewed mostly by American sailors.

Before World War I the U.S. relied on a combination of U.S.- and foreign-flagged vessels for both international and domestic shipping. But when the war broke out, foreign ships withdrew from American routes to aid war efforts in their own countries. The sudden shortfall sent shock waves across U.S. ports and domestic trade routes.

Congress enacted the Jones Act in hopes of reducing America’s reliance on foreign mariners. In theory it was meant to ensure stable supply lines within the United States and bolster domestic shipbuilding to ensure an inventory of U.S. merchant marine vessels and trained American mariners that could be tapped to support U.S. operations in the event of another conflict.

But today there are fewer than 100 Jones Act- compliant vessels in the country, with most oil tankers in particular committed to routes that don’t include Hawaii. That has meant Hawaii has mostly relied on foreign tankers, which cannot legally transport oil between American ports and are limited to only delivering oil from overseas in the islands.

The tankers offload crude oil into storage tanks in West Oahu through offshore mooring systems and load refined products at Honolulu Harbor terminals onto fuel barges to be taken to neighbor islands. According to the U.S. Energy Information Administration, the majority of crude oil that currently comes to Hawaii is from Libya, Argentina and Brazil.

That crude oil goes to Par Hawaii Refining LLC in Kapolei, which operates the only refinery in the state and refines it to meet Hawaii’s demands — including powering most of the state’s electrical grid. Hawaii also imports pre-refined petroleum products, including jet fuel, propane, low-sulfur diesel fuel and motor gasoline from countries in Asia, the Caribbean and South America.

According to the U.S. Energy Information Administration, the transportation sector uses almost two-thirds of all petroleum consumed in Hawaii, power plants use about 25% and the combined industrial, commercial and residential sectors make up the remaining 10% of petroleum use.

“It is too early for us to know how this particular requirement will affect Hawaii until there are more details and parameters are set from the administration,” said Par Hawaii spokesman Marc Inouye. “We are closely monitoring this and other proposed taxes and tariffs that may impact energy security and assurance for our islands.”

In 2015, Hawaii became the first state to pledge to work toward powering the state with 100% renewable energy by 2045, both to fight climate change and make the islands more self-­sufficient — but that has come with challenges of its own. Planned solar farm and battery storage projects have faced delays or cancellation.

Trump has been outspoken in his opposition to solar and wind farms and promised to increase oil production and consumption. Among his first actions as president was an executive order that stopped further consideration of leasing federal waters, at least temporarily, for wind energy projects nationwide pending a comprehensive review by his administration. That has indefinitely stalled a controversial plan for an offshore wind farm off Oahu.

The state is also looking into the potential of using liquefied natural gas as a “bridge fuel” to lower emissions during the shift to renewable sources, potentially building a new facility where Oahu’s demolished coal plant had been. It would require significant infrastructure investments and faces logistical hurdles — including shipping.

“Even if they shift it over to LNG, that’s not going to lessen our dependence on foreign fuel sources either, because there’s no LNG carriers in the Jones Act fleet,” Coleman said. “That would definitely have to come from foreign suppliers, like they do for New England and Puerto Rico. I mean, we would be able to buy it, but we wouldn’t be able to buy it from American sources. Even though America is (one of the) largest exporters right now of fuels, oil and LNG … none of it comes to Hawaii.”

Supporters of the Jones Act maintain that it guarantees reliable shipping lanes from the mainland to Hawaii and helps to support jobs both in ports and on ships for American workers — including Hawaii residents — and protects those jobs from predatory practices that would undercut American companies and merchant mariners.

Many maritime companies are known to register their ships in other countries, making the operations of the boats subject to the laws and regulations of the flag state — a practice known as using “flags of convenience.” International shipping companies and cruise line operators commonly register their ships with flag states that have weaker labor, safety and environmental regulations — or with governments willing to look the other way when they cut corners or break the law. This often allows them to cut costs even as they face accusations of labor abuse and reckless behavior around the world.

But even goods arriving in Hawaii on Jones Act-­compliant ships could get more expensive if the Trump administration decides to tax foreign-flagged ships, warns Carl Bonham, executive director of the University of Hawaii Economic Research Organization.

“Remember, even the goods shipped to Hawaii by Matson and Pasha, or for that matter air cargo at some point, involved goods shipped to U.S. ports on foreign-­flagged vessels,” Bonham said. “For example, a Hyundai car made in South Korea would likely get shipped to the U.S. on ships owned by Hyundai or any number of other foreign-­owned vessels. When those cars come to Hawaii on a U.S.-flagged ship, the tax costs would still come with them if they are not absorbed by the original manufacturer or shipper.”