A law designed to protect American ship-building is limiting aid delivery to Puerto Rico

In the aftermath of hurricane Maria, Puerto Rico is dealing with horrifying devastation. One thing that could help with a recovery that’s bound to be long and difficult is opening the ports to emergency-supply-laden foreign boats. Plenty such boats come and go to the US that could be deployed for that task, but there’s a catch: They’re not allowed to unload their wares on the island.
Under a long-standing US law, the 1920 Merchant Marine Act, all the transportation of goods between US ports has to be done by US vessels exclusively. This means that ships from other countries can’t transport supplies between US harbors. That limits the number of available boats, even in unusual, extreme situations such as what Puerto Rico is experiencing now.
In the wake of past natural disasters, the US has temporarily lifted the rule, known as the Jones Act after its sponsor, senator Wesley Jones. The Department of Homeland Security did that earlier this month in response to hurricanes Harvey and Irma, which hammered the Gulf and Atlantic Coasts.

https://qz.com/1087325/what-is-the-jones-act-and-how-is-it-affecting-puerto-ricos-hurricane-recovery/