The International Maritime Organization (IMO) is working on the adoption of a greenhouse gas (GHG) pricing instrument to decarbonise international shipping. This article analyses whether World Trade Organization (WTO) law can limit the implementation of an IMO GHG pricing instrument. In particular, it breaks new ground by analysing the compatibility of current proposals tabled at the IMO with the General Agreement on Trade in Services and the General Agreement on Tariffs and Trade. In addition, it analyses whether WTO law limits the IMO's ability to adopt a GHG pricing instrument that addresses equity concerns via the implementation of exemptions for developing countries, Least Developed Countries, and Small Islands Developing States.