The International Maritime Organization’s landmark climate deal to slash greenhouse gas emissions from global shipping has been thrown into uncertainty after Washington warned it would penalize countries that support the pact.

The Net-Zero Framework, which has been nearly a decade in development, is designed to bring the global shipping industry to net-zero emissions by mid-century. The agreement has broad backing from industry stakeholders and many IMO member states and had been on track for formal adoption next week.

But in August, the Donald Trump administration issued a rare joint statement from four cabinet secretaries announcing U.S. opposition to the plan. Since then, Washington has signaled it could use tariffs and other economic measures to penalize countries that vote in favour of the deal.

Caught between competing interests, Antigua and Barbuda’s prime minister Gaston Browne has confirmed that the country will abstain from voting on a proposal to reject the framework. He says as advocates for climate change, his country cannot vote against it and in the face of deferral, they will be forced to abstain.

The final vote later this week is expected to be closely watched, with Washington’s threats raising the stakes for what was expected to be a smooth adoption of a historic climate accord.