The allegations follow the detention of the 32,300-dwt King Yukon(built 2009), which was held in New Orleans after port inspectors determined the ship had failed to switch to low-sulphur fuel when it entered an environmentally sensitive zone known as the North American emission control area (ECA).

Under Annex VI of the International Convention for the Prevention of Pollution from Ships (Marpol), vessels sailing within 200 nautical miles of the US coast are required to burn bunkers that boast a sulphur of no more than 1%.