This bill amends the Internal Revenue Code of 1986 to expand an existing excise tax exemption for alternative motorboat fuels. It extends the current exemption, which applies to such fuels sold as supplies for vessels or aircraft, to cover a new category of maritime operations. Specifically, the legislation will apply the exemption to fuel sold for use by vessels that are engaged in trade exclusively between the Atlantic or Pacific ports of the United States , including any U.S. territory or possession. This change aims to provide tax relief for these specific coastal shipping operations and will take effect for fuel sold or used after December 31, 2025 .