As the IMO mid-term measure intends to regulate GHG intensities of fuels used by ships on the high seas, permissibility of the exercise of port state jurisdiction on non-Party ships may be questioned. Based on discussions regarding the “maritime EU-ETS”, such port state measures are deemed extra-territorial application of prescriptive jurisdiction, which could be based on article 218 of UNCLOS. However, universality principle would more appropriately serve as the basis for this international rule to address climate change, which is a “common concern”. Port state control provides an important function for ensuring a level-playing field and the GHG reduction targets.