The Department of Homeland Security is under pressure from members of Congress to waive the Jones Act, a law that dates back to 1920 in order to speed up the shipment of goods and commodities to Puerto Rico as it deals with a humanitarian crisis after Hurricane Maria.

The Jones Act requires that all goods shipped between U.S. ports be carried by ships built by Americans and operated by Americans. Under the law, foreign vessels that enter Puerto Rico are subject to taxes, fees and tariffs.

On Monday, a group of eight House Democrats asked that DHS waive the law for one year for Puerto Rico.

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"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," said a letter, spearheaded by Reps. Nydia Velazquez of New York, Luis Gutierrez of Illinois and Jose Serrano of New York.

Separately, Sen. John McCain, R-Arizona, sent a similar letter to Acting DHS Secretary Elaine Duke on Tuesday urging that the law be waived and arguing that it should ultimately be repealed. McCain said that the emergency waivers are valuable in speeding up recovery efforts.

"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," he wrote. "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."

Senior DHS officials said Wednesday that the department has not received any formal requests to waive the Jones Act, although they acknowledged receiving the request from the group of House lawmakers. They claimed they hadn't received any from senators despite McCain's letter. These officials also stressed that the Jones Act is not interfering with the Defense Department's and FEMA's efforts to get goods and commodities to the island. They said the challenge is moving those things around Puerto Rico.

President Trump, however, seemed to offer a different reason that there had been no waiver. As he was departing for Indiana, a reporter asked Mr. Trump why the Jones Act had not been waived for Puerto Rico, as it had been for Texas.

"Well, we're thinking about that," he responded. "We have a lot of shippers and a lot of people that work in the shipping industry that don't want the Jones Act lifted. We have a lot of ships out there right now."

And, in fact the American Maritime Partnership (AMP), which is the lobbying arm of the U.S. flag shipping industry, said on its website that a waiver "could hinder, not help relief efforts." It also suggested it "could overwhelm the system, creating unnecessary backlogs," and it could cause "confusion on the distribution of critical supplies throughout the island."

Meanwhile, while testifying before the Senate Homeland Security Committee Wednesday morning, Duke was asked about the Jones Act in regards to Puerto Rico.

"In terms of the Jones Act waiver, we have researched this -- I read it in the news clips this morning -- we have no known Jones Act waiver requests. We did receive a congressional letter today. We are double-checking to make sure it isn't true," Duke said. "There's two issues with Puerto Rico. One is the potential shortage of carriers with the U.S. flag carriers. The second is tariffs and other things that make the fuel cost high in Puerto Rico, and that's what we're hearing, too, that people are suffering from the tariffs."

McCain tweeted Wednesday that a Jones Act waiver request had been denied by DHS, but that claim was disputed by the senior DHS officials. The officials explained that the ability for DHS to issue waivers, based on the law, is constrained. The only reason DHS can use to issue a waiver is that it has to be in the interest of national defense, the officials said. It can't grant one to make costs cheaper. There are two ways for a request to be made: either the Secretary of Defense has to make a request to waive it or if a request comes from other federal agencies, DHS has to consult with the Maritime Administration on the availability of qualified shipping vessels.

A waiver had been granted for two weeks earlier this month after the Defense Department requested that one be issued following Hurricane Harvey that hit Texas. That waiver, which also applied to Puerto Rico, expired last Friday.

While the letter from the group of House lawmakers was sent Monday, the senior DHS officials said that they had just received it and DHS general counsel are evaluating whether members of Congress have standing to issue such requests for a waiver.

Senior DHS officials said it's "unlikely" that a waiver would be granted Wednesday.