A tariff or import tax is a duty imposed by a national government, customs territory, or supranational union on imports of goods and is paid by the importer. (Exceptionally, an export tax may be levied on exports of goods or raw materials and is paid by the exporter.) Besides being a source of revenue, import duties can also be a form of regulation of foreign trade and policy that burden foreign products to encourage or safeguard domestic industry. 'Protective tariffs' are among the most widely used instruments of protectionism, along with import quotas and export quotas and other non-tariff barriers to trade.