The Jones Act will be waived "immediately", press secretary Sarah Huckabee Sanders said.
President Trump is slated to visit Puerto Rico and the U.S. Virgin Islands next Tuesday, but he has been roundly criticized for the slowness of Washington's response to the island's plight.
Last night, the chairman of the American Maritime Partnership told CBS4 News, shippers were not in favor of waiving the act.
More than 90% of cellular communication sites remain out of service, U.S. officials say.
The most powerful hurricane to hit Puerto Rico in almost 90 years, Maria swept across the island last Wednesday.More news: Venezuelan-Americans support country being added to list with travel restrictions
The Trump administration initially insisted the waiver was not needed because the USA had enough ships to deliver goods but an unnamed official from the Department of Homeland Security warned there was a bottleneck with unloading cargo at the island's damaged ports and getting supplies inland, as well as a shortage of diesel fuel. The entire island is in a communications and power blackout, Washingon Post reporters there say: "Estimates for the return of electricity and basic services will be measured not in days but in weeks and months".
Reports of isolated USA citizens struggling in the heat without electricity and running low on food and water have now spurred the Pentagon to throw resources into the relief effort even though they haven't been specifically requested by territorial officials.
Trump faced mounting calls to freeze the 97-year-old act, which requires products shipped between USA ports to be moved by American-owned ships.
In signing a 10-day waiver that covers all products being shipped to Puerto Rico, Department of Homeland Security acting Secretary Elaine Duke side-stepped that controversy.
But a shortage of truckers and the island's devastated infrastructure are making it tough to move aid to where it's needed most.
Critics of the law call it a protectionist relic, and the Wall Street Journal editorialized this week that it should be permanently repealed.More news: Iran launches new ballistic missile
"The food is here, the water is here".
"We've got to just keep being creative and thinking, OK, so what are the needs?"
Military personnel are playing a sizeable role.
Apparently stung by the criticisms, administration officials have emphasized the complexity of delivering aid to the island.
It also was shipping a large generator to power a radar center to help air traffic control in San Juan and other airports. Also on the way are ambulances and 100 trucks carrying diesel and gasoline fuel. "You have to remember that not only did Irma come through and create quite a bit of damage and destruction that we were working to fix, but Maria was. one of the strongest storms that Puerto Rico's seen since the 20's and let's face it, the infrastructure is weak and there were no building codes and so there is a lot of devastation and we understand that".
As the humanitarian crisis in Puerto Rico spirals, Sen.More news: Facebook releasing 3000 Russian-bought adverts to Congress