The 1920 Jones Act requires Puerto Rican ports only do business with American ships, prohibiting deals with many of the island’s Latin American neighbors and giving American shipping companies almost total control of prices.
The Jones Act is pretty bad, yes, but that’s just nonsense. For it covers movements between American ports and American ports only. So, trade between Puerto Rico and the Dominican Republic, as an example, is entirely unaffected.
Please, get these things right, they’re important.
Bonus point, the Jones Act is very like the Navigation Acts that we Brits imposed upon the colonials: you know, one of the things the Revolutionary War was all about?