There are two sorts of trade restrictions which are applied in the name of 'environmental protection': we term these 'unilateral' or 'pursuant' measures. In simple terms, unilateral restrictions are unashamedly taken to satisfy a domestic agenda while pursuant measures are so named because they are applied pursuant to a multilateral environmental agreement. Thus southern African countries and the USA, for example, are united in their refusal to accept commercial imports of Appendix-I CITES species.

Unilaterally-imposed trade restrictions have always been a major tool to effect change in policy and some observers would claim that there cannot be multilateralism without unilateralism because in a world where different members of the international community hold alternative views, unilateral measures, power-based measures are necessary to bring all parties to the negotiating table. It is, for example, often stated that slavery only came to an end because of unilateral action. The WTO, however, is designed to turn a power-based system to one based on rules in which unilateralism is unwelcome - and this is clearly to the benefit of the developing world.

Unilateral trade restrictions fall into one of three categories (Table 1). They may be direct restrictions on trade (such as the U.S. ban on harp seal products). In this case they run counter to Article XI unless they meet the terms of the Article XX exemptions. They may relate to a characteristic of the product, such as its packaging, which is termed a product standard. If the restrictions discriminate against other producers then they are counter to Article III. Even where they are not discriminatory, agreements such as that on Technical Barriers to Trade (TBT) may make them WTO illegal. Finally, restrictions might be introduced, not because of a characteristic of the product, but because of the way it was produced. This is termed a restriction related to production and process method (PPM) standards. The majority of objections to imports on environmental and animal welfare grounds are to do with the way the item is produced.