Non-tariff barriers to trade (NTBs) are trade barriers that restrict imports but are not in the usual form of a tariff. Some common examples of NTB’s are anti-dumping measures and countervailing duties, which, although they are called “non-tariff” barriers, have the effect of tariffs once they are enacted. Their use has risen sharply after the WTO rules led to a very significant reduction in tariff use. Some non-tariff trade barriers are expressly permitted in very limited circumstances, when they are deemed necessary to protect health, safety, or sanitation, or to protect depletable natural resources. In other forms, they are criticized as a means to evade free trade rules such as those of the World Trad Organization (WTO), the European Union (EU), or North American Free Trad Agreement (NAFTA) that restrict the use of tariffs.