(1) Quotas Explanation: Non-tariff barriers to trade (NT13s) are trade barriers that restrict imports but are not in the usual form of a tariff. Some common examples of NT13's are anti-dumping measures and countervailing duties. Which, although they are called "non-tariff' harriers, 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.