The American Mariner Tax Fairness Act would amend the tax code to treat income earned by U.S. merchant mariners as foreign earned income, allowing them to qualify for the foreign earned income exclusion. Under current law, this exclusion is generally available only to U.S. citizens and residents who live and work abroad, but this bill would extend it to mariners who work at least 90 days per year on qualifying U.S. vessels engaged in foreign trade. Qualifying vessels are defined as self-propelled U.S. flag ships of at least 6,000 deadweight tons used exclusively in international commerce. The bill would apply to tax years beginning after its enactment, with no specific funding requirements or sunset date specified. This change would reduce federal income taxes owed by eligible merchant mariners on their maritime earnings.