The Clean Shipping Act of 2023 would establish federal standards to reduce greenhouse gas emissions from commercial vessels operating in U.S. waters or between U.S. and foreign ports. Starting in 2027, vessels would be required to progressively cut the carbon intensity of their fuel, reaching a 20 percent reduction by 2029, 45 percent by 2034, 80 percent by 2039, and achieving complete zero-emission fuel by 2040. The Environmental Protection Agency would finalize these standards by 2026 and adjust them if necessary based on technological and economic feasibility. The legislation also requires vessels to monitor and annually report their fuel carbon intensity and emissions to the EPA, with the agency publishing public reports on shipping industry progress. The bill applies to commercial vessels of at least 400 tons and includes an in-port emission standard requiring vessels at U.S. berths and anchorages to eliminate greenhouse gas and air pollutant emissions by 2030, with similar feasibility adjustments allowed.