In late fall, a groundbreaking global agreement to reduce emissions from the maritime industry seemed on the verge of approval. More than 100 nations were prepared to support the plan, which aimed to curb pollution from cargo vessels — one of the fastest-growing sources of greenhouse gases. Yet just before the vote, the United States intervened with an aggressive diplomatic pressure campaign that stunned many foreign officials and ultimately halted the deal, according to nine diplomats who were directly involved in the negotiations.

Multiple diplomats from Asia, Europe and developing nations described private warnings that were conveyed with unusual bluntness. An ambassador from Asia recounted being told that his country’s seafarers could lose permission to disembark at U.S. ports if he supported the proposal. Caribbean representatives said they were informed they could be blacklisted from entering the United States. Several diplomats said Secretary of State Marco Rubio personally contacted foreign officials, threatening financial consequences and other penalties if they did not side with Washington.

These reported threats, which included visa restrictions, sanctions, and tariff retaliation, prompted several nations to reverse course and blocked the agreement from advancing. All nine diplomats who described the pressure effort requested anonymity, citing fear of retaliation by the Trump administration.

U.S. officials strongly denied that personal intimidation tactics were used. In statements, the White House, the State Department, and the Energy Department acknowledged lobbying against the deal, but insisted their efforts were based on policy disagreements, not threats. They argued that the proposed fee on high-polluting ships would have damaged the American economy and unfairly burdened U.S. consumers and industries.

A senior State Department official confirmed the U.S. had coordinated with Saudi Arabia to oppose the measure, asserting that Washington’s stand encouraged other skeptical nations to break from the consensus. But foreign diplomats described the American pressure as unusually confrontational, disproportionately targeting small and economically vulnerable countries with close ties to the United States. Several said they were summoned to the U.S. Embassy in London for tense discussions.

The proposed agreement had been years in the making within the International Maritime Organization (IMO), the United Nations agency responsible for global shipping rules. It would have introduced a pollution fee for vessels with high carbon emissions, gradually tightening standards to accelerate the industry’s transition from oil-based fuels to cleaner alternatives. Major nations — including Britain, Canada, Japan, China, and the European Union — supported the plan. U.S. officials had previously backed similar efforts until the Trump administration returned to power.

David Goldwyn, a former U.S. diplomat who served in the Obama and Clinton administrations, called the tactics attributed to the Trump administration excessive. In his view, the issue did not justify the level of diplomatic force allegedly deployed. “This was hardly a matter of national security,” he remarked. “Using threats for a climate pollution vote is like deploying military firepower over a minor infraction.”

The Trump administration has consistently rejected global climate frameworks it believes would harm fossil fuel interests and limit U.S. energy dominance. Promoting U.S.-produced oil, gas and coal remains a central part of its policy agenda. Senator Sheldon Whitehouse of Rhode Island, briefed on the events by participants, likened the U.S. approach to intimidation, referring to it as a “shock-and-awe style coercion.”

These revelations surfaced as world leaders gathered in Brazil for United Nations climate negotiations. For the first time in three decades, the United States did not send senior representatives to the talks and signaled it may not even dispatch technical staff. President Trump has also continued efforts to exit the 2015 Paris climate accord, which he frequently dismissed in stark terms.

Senior administration officials defended their stance, emphasizing that they clearly outlined potential consequences for nations supporting what they called activist-driven climate rules. They argued that imposing universal shipping fees would raise global consumer prices and hinder trade. A White House spokesperson said the IMO, not the United States, attempted to “pressure nations into a flawed policy.”

Foreign officials, however, described events differently. Some called the diplomatic push unprecedented, claiming officials from Caribbean and Pacific regions felt particularly threatened. One European diplomat recounted hearing that the Philippines was warned its sailors could be barred from entering American ports if it supported the measure. Another said a Jamaican negotiator was told he could lose the ability to travel to the United States altogether.

The shipping industry accounts for roughly three percent of global greenhouse gas emissions — comparable to aviation — and is projected to grow significantly without intervention. With ships transporting about 90 percent of global trade, the stakes were high. The proposed fee had the backing of many major shipping firms that viewed the plan as a practical step toward long-term decarbonization.

Energy Secretary Chris Wright later described the administration’s campaign as a strategic opportunity. Speaking at a policy forum, he recalled recognizing early that defeating the measure would capture President Trump’s interest. He said he personally contacted officials from around 20 countries, with Secretary Rubio and Commerce Secretary Howard Lutnick also making calls.

The United States intensified its efforts as the vote approached. During meetings in Brussels, European officials reported that American representatives challenged their commitment to the plan and questioned the European Union’s authority. Days before the scheduled vote, top U.S. officials released public warnings that countries backing what they described as “European-led climate regulation” could face visa restrictions, trade fees, and other penalties.

Ultimately, on October 17, the vote did not proceed as expected. Instead, the IMO agreed to postpone the decision for one year, effectively freezing the proposal indefinitely. Administration officials celebrated the outcome, characterizing it as a victory against what they called a global carbon tax.

While the United States has historically exercised influence over international policy — regardless of which party holds power — experts noted that direct threats against diplomats would represent a new and highly unusual step. Richard Fontaine, head of a conservative national-security think tank, said he could not recall a similar instance of the U.S. explicitly threatening to revoke visas based on a foreign government’s vote in an international body.

After the vote, Secretary Rubio published an opinion piece praising the administration’s diplomatic strategy and warning that similar efforts would be mounted against future climate initiatives emerging from the U.N. system.

As the maritime sector faces mounting pressure from scientists, governments, and industry players to address emissions, the collapse of the shipping deal represents a significant setback for global climate efforts — and a striking example of how geopolitical power struggles are reshaping environmental diplomacy.