Русско-англо-русский юридический словарь

A common external tariff must be introduced when a group of countries forms a customs union. [...] It is designed to end re-exportation; but it may also inhibit imports from countries outside the customs union and thereby diminish consumer choice and support protectionism of industries based within the customs union. (Wikipedia)

For example, each country within a customs union has the same tariff rate on imports from countries outside the customs union. (Global Trade Policy: Questions and Answers by Pamela J. Smith, Google Books)