The "Merchant Marine Allies Partnership Act" aims to expand participation in U.S. coastwise trade by allowing vessels, owners, and crews from allied foreign countries to engage in certain domestic shipping activities. This legislation introduces significant amendments to Title 46, United States Code, creating specific exceptions to existing coastwise laws.

A central component of the bill is the establishment of a Foreign Ally Shipping Registry, to be maintained by the Secretary of State in consultation with the Commandant of the Coast Guard. This registry will list countries determined to be allies for the purpose of carrying out coastwise trade, with all NATO member countries automatically included unless otherwise removed. The Secretary of Transportation is authorized to grant waivers, for periods up to five years and renewable, allowing "qualified vessels" from these allied nations to transport merchandise between points in the United States.

A vessel qualifies if it is wholly owned by nationals or the government of a registered allied country (or jointly with a U.S. national) and flagged in the U.S. or an allied country. Furthermore, the bill exempts crew members who are nationals of the U.S. or an allied country, working on these authorized qualified vessels, from certain U.S. citizenship and credentialing requirements. Procedures are also outlined for the removal of countries from the registry, including immediate removal upon a declaration of war by Congress.

Finally, the bill amends the Tariff Act of 1930 to provide an exemption from duties on repairs. Specifically, U.S. documented vessels will not incur duties for repairs made in shipyards located in countries listed on the Foreign Ally Shipping Registry. This provision further incentivizes collaboration with allied nations in maritime maintenance and operations.