The US has warned of retaliatory measures against nations supporting a proposed carbon emissions tax for shipping, as the UN's International Maritime Organization (IMO) works to adopt it's Net-Zero Framework, reports New York's FreightWaves.

The US State Department called the plan a "European-led neocolonial export of global climate regulations" and said it would not accept any agreement that unfairly burdens American interests. The IMO vote is scheduled for October 14-17 in London.

Under the proposal, vessel operators must report greenhouse gas emissions annually. Ships exceeding limits will pay fees, while those using cleaner fuels will receive incentives. The IMO would collect revenues through a Net-Zero Fund.

The US warned it may block vessels from its ports, impose visa restrictions on crews, and apply penalties to government contracts and liquefied natural gas terminals. Additional port fees and sanctions on officials backing climate policies are also being considered.

The statement was signed by Secretary of State Marco Rubio, Secretary of Energy Chris Wright, and Secretary of Transportation Sean Duffy. They urged IMO members to reject the Net-Zero Framework and prioritise economic and energy security.

Ocean carriers have already taken steps to reduce emissions. About 41 per cent of containerships on order are designed for alternative fuels such as liquefied natural gas or ammonia. The largest ships account for 85 per cent of sector emissions.

Nearly all ocean-going ships are built outside the US, with 51 per cent in China, 28 per cent in South Korea, and 15 per cent in Japan. The US reversal on IMO cooperation echoes its stance on the International Criminal Court, which it helped develop but never ratified.