Leading shipping companies are warning that the International Maritime Organization’s (IMO) proposed net zero framework could saddle the sector with more than $300 billion in costs by 2035 if targets are missed.

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The IMO, which regulates global shipping, is preparing to adopt new rules next month requiring vessels to pay levies on at least part of their greenhouse gas emissions. The framework is central to the IMO’s pledge to achieve net zero emissions by 2050 but has already drawn criticism. The U.S. government has dismissed the plan as a “global carbon tax.”

In a joint statement, shipowners representing more than 1,200 vessels estimated annual compliance costs could reach $20–30 billion by 2030 and surpass $300 billion by 2035 if the global fleet falls just 10% short of its decarbonization targets.

While the U.S. remains opposed, most countries voted in favor of the framework earlier this year, and the International Chamber of Shipping — representing over 80% of the world’s merchant fleet — has endorsed it.

Still, industry leaders argue the current design of the Net Zero Framework (NZF) risks undermining both decarbonization efforts and competitiveness. “It is essential that the IMO NZF implements GHG measures that are fit for purpose,” said the group, which includes Stolt Tankers, Frontline Plc, and Saudi Arabia’s Bahri. The statement urged amendments to ensure “realistic trajectories” and warned against “excessive financial burdens and inflationary pressure to the end-consumer.”

The upcoming IMO decision will be a pivotal moment for global shipping, shaping both the pace of decarbonization and the cost burden shouldered by carriers and their customers.