The article deals with the EU rules on prohibition of fiscal barriers within the internal market, and the free movement of goods. Prohibition of fiscal barriers which form an obstacle to free movement of goods are regulated by prohibition of customs duties and prohibition of discriminatory taxation. Both these fiscal levies must follow the non-discrimination principle, i.e. the way these levies are applied must respect the principle of prohibition of discrimination based on nationality. It is also important to make difference between the prohibition of customs duties and prohibition of discriminatory taxation as they are subject to different legal regime.