The Sustainable International Financial Institutions Act of 2025 aims to align United States foreign financial policy with global climate goals. It requires U.S. Executive Directors at specified international financial institutions (IFIs) to actively use their voice and vote to advance the global transition to a clean energy economy and reduce greenhouse gas emissions, including by channeling assistance towards countries building sustainable energy systems. The bill mandates that these U.S. Directors oppose any policy, investment, loan, or financial assistance that would create new or expand existing fossil fuel activity , including the refurbishment or life extension of current fossil fuel capacity. It also specifically calls for supporting the phasing out of funding for internal combustion engines in passenger vehicles and buses by 2031. The legislation broadly defines "fossil fuel activity" to encompass exploration, production, transportation, combustion, and related infrastructure for coal, oil, and natural gas. To enforce these directives, the bill establishes a mechanism where the U.S. Secretary of the Treasury must determine the amount of IFI funding for new fossil fuel capacity annually. The U.S. contribution to any such IFI will be reduced by that amount, with the funds deposited into an escrow account . These escrowed funds will only be released to the IFI once it certifies that it is no longer providing support for new fossil fuel activities. Beyond IFIs, the bill enacts a direct prohibition on the United States government providing any loan, insurance, guarantee, or financial or technical assistance, directly or indirectly, for any fossil fuel activity or related infrastructure project. This prohibition applies to various U.S. agencies, including the United States International Development Finance Corporation, the Export-Import Bank, and the United States Agency for International Development.