The Marine Mammal Protection Act of the United States of America (MMPA) banned importations of yellowfin tuna caught in purse-seine nets in the Eastern Tropical Pacific Ocean. Based on the MMPA, in 1990 the US Government prohibited imports of yellowfin tuna harvested in the said marine area by Mexican vessels, unless the corresponding importer declared that none of its products had been harvested with purse-seine nets.
A GATT panel was established on February 1991, at request of the Mexican Government to settle the dispute. Mexico argued that the import embargos imposed by the USA were restrictions on importation inconsistent with USA obligations under GATT Article XI (General elimination on Quantitative Restrictions).
Conversely, the USA said that the former were measures that constituted an enforcement at the time or point of importation of the requirements of the MMPA, and were therefore permitted, and also allowed under GATT Article XX (b) and XX (g), which provided a general exception from GATT obligations for measures “necessary to protect human, animal or plant life or health” and “relating to the conservation of exhaustible natural resources”, respectively.
The Panel held that the afore-mentioned prohibition of imports was contrary to GATT Article XI:1. According to the Panel, it was true that GATT parties were allowed to impose internal regulations on imported products, on a non-discriminatory basis. Nevertheless the Panel considered that the MMPA regulated the harvesting of tuna, but not tuna as a product.
The Panel also held that Articles XX (b) and XX (g) could not be applied to the case because of their restricted scope of jurisdiction. Regarding this mater, the Panel established that the said articles were intended to protect the life and health of humans, animals and plants, as well as to regulate the consumption of exhaustible natural resources within the jurisdiction of the importing country (the USA).
The Panel entitled GATT contracting parties to impose non-discriminatory taxes or regulations that served environmental purposes, but prevented them from restricting imports of a country that had different environmental policies.