encumbrance to trade which, whatever its formal description or the technique employed, has the same effect as a direct restraint, whether partial or total, on imports, exports or goods in transit
... the following shall be prohibited: - the levying of any charge having effect equivalent to a customs duty; - the application of any quantitative restriction or measure having equivalent effect, subject to the provisions of the Protocol on the Grand Duchy of Luxembourg. The restriction of import licences to a specified category of those entitled to receive them shall be one of the measures considered as having effect equivalent to a quantitative restriction.
