The UN can't tax the US.
Cool straw man though.
The IMO/UN can't unilaterally tax sovereign nations (per UN Charter limits), but the levy would function like one via market pressures.
The International Maritime Organization (IMO), which is a specialized UN agency focused on global shipping regulation attempted to advance a global emissions pricing mechanism—often framed by U.S. officials as a de facto "carbon tax"—that would have indirectly raised costs for U.S. shipping companies, consumers, and trade. This effort culminated in a failed vote during an extraordinary IMO session on October 14-17, 2025, largely due to aggressive U.S. opposition.
Estimates suggested it could add up to 10% to global shipping costs, indirectly hiking prices for U.S. imports/exports (e.g., consumer goods, energy). U.S. critics, including the Trump administration, called it "taxation without representation" since revenues wouldn't return to the U.S. Treasury but to a UN fund.
The IMO lacks direct enforcement power since member states must ratify and implement via national laws, but non-compliance could lead to port access restrictions or trade barriers.
Singapore proposed a delay motion (backed by Saudi Arabia), which passed on October 17, postponing adoption to at least October 2026 (with implementation possibly slipping to 2030). U.S. officials hailed it as a "huge win," crediting President Trump's leadership.