A woman trying to leave her house in Salinas, Puerto Rico, last week. Carlos Garcia Rawlins/Reuters Puerto Rico was devastated by Hurricane Maria, and some experts say a 100-year-old US law has slowed its recovery.

The law, known as the Jones Act, places heavy tariffs on foreign ships delivering goods to the US island territory.

President Donald Trump on Thursday waived the act, the White House said.

Puerto Rico is reeling in the aftermath of Hurricane Maria — the most powerful storm to hit the island since 1928 — and the Trump administration on Thursday waived a law that many lawmakers and economic experts had said was hampering the island's recovery.

The Merchant Marine Act of 1920, known as the Jones Act, was passed after World War I in an effort to protect the US maritime industry from foreign competition by requiring that only US ships — built, staffed, and owned by Americans — carry goods between domestic ports.

That means any foreign ships delivering goods to Puerto Rico — a US territory — are subject to steep tariffs, driving up the prices of consumer goods.

President Donald Trump took action Thursday, waiving the act temporarily for Puerto Rico at the request of its governor. The White House said the waiver could take effect immediately.

Goods shipped from the US mainland to Puerto Rico — often transferred from foreign ships onto US vessels in Florida — are double the price they are in neighboring islands, including the US Virgin Islands, not subject to the Jones Act. It makes the cost of living in Puerto Rico, where the per capita income is less than half that of the poorest state in the US, significantly higher than in most American cities.

"This is a shakedown, a mob protection racket, with Puerto Rico a captive market," Nelson Denis, a former New York state assemblyman, wrote in a Monday New York Times op-ed article.

With Puerto Rico in dire straits, critics of the law have argued that the government should repeal it altogether, automatically suspend it during natural disasters, or provide far-flung places like Alaska, Hawaii, and Puerto Rico with permanent waivers.

The Trump administration recently granted temporary waivers in Texas and Florida following Hurricane Harvey and Hurricane Irma.

"A humanitarian crisis is about to explode in Puerto Rico. But the consequences of Jones Act relief would be immediate and powerful," Denis wrote. "This is not the time to price-gouge the entire population."

Critics argue that the law also places burdensome restrictions on US businesses, which are subjected to higher costs of US shipping, and consumers. But the maritime industry — represented by powerful lobbying groups — is strongly in favor of maintaining the status quo.

"Almost every study shows that the losses to consumers are much bigger than the gains to anybody else," Tom Grennes, a professor of economics emeritus at North Carolina State University, told Business Insider.

But while the gains are concentrated in the shipping industry, the losses are spread thin — in mainland America, they amount to about $5 a US citizen each year.

Presidents including Ronald Reagan and Barack Obama have supported the law for national security reasons, arguing that US reliance on foreign shipping could be dangerous in a crisis. But the US fleet is shrinking, so Grennes says this defense of the law is increasingly irrelevant.

On Wednesday, Trump told reporters that he was "thinking about" granting Puerto Rico a Jones Act waiver. But he quickly added, "We have a lot of shippers and a lot of people who work in the shipping industry that don't want the Jones Act lifted, and we have a lot of ships out there now."

While the Jones Act is in line with Trump's "Buy American, Hire American" motto, it is also a form of regulation — which Trump has pledged to cut — and, in some cases, burdens the energy industry.

Trump has been criticized for appearing to be less attentive to Puerto Rico, which he described as "absolutely obliterated" by the storm, than to Texas and Florida following hurricanes Harvey and Irma.

The president's first public response to Hurricane Maria came in a series of tweets in which he focused on the island's weak infrastructure and economy five days after the storm hit.

A woman receiving water and food from National Guard troops in San Juan, Puerto Rico, on Sunday. Carlos Giusti/AP

A handful of US lawmakers have long argued for a repeal of the Jones Act.

In July, Republican Sen. John McCain, a longtime foe of the Jones Act, introduced legislation that would repeal the law, which he argues "hinders free trade, stifles the economy, and ultimately harms consumers." The senator renewed his call to action this week.

"I am very concerned by the department's decision not to waive the Jones Act for current relief efforts in Puerto Rico, which is facing a worsening humanitarian crisis following Hurricane Maria," McCain wrote in a letter to the Department of Homeland Security on Tuesday.

"It is unacceptable to force the people of Puerto Rico to pay at least twice as much for food, clean drinking water, supplies and infrastructure due to Jones Act requirements as they work to recover from this disaster," he added. "Now, more than ever, it is time to realize the devastating effect of this policy and implement a full repeal of this archaic and burdensome act."

Eight Democratic members of Congress, including Reps. Nydia Velázquez of New York and Luis Gutiérrez of Illinois, have also spoken out, calling for a one-year suspension of the law to speed Puerto Rico's recovery.

"The island is now facing an unprecedented uphill battle to rebuild its homes, businesses and communities," Velázquez and the other representatives said in a letter to DHS on Monday. "Temporarily loosening these requirements — for the express purpose of disaster recovery — will allow Puerto Rico to have more access to the oil needed for its power plants, food, medicines, clothing, and building supplies."