THAT ACCORDING TO THE CONSISTENT CASE-LAW OF THE COURT EVEN THE POTENTIAL EFFECTS OF A NATIONAL MEASURE MAY RENDER IT INCOMPATIBLE WITH THE TREATY . AS FAR AS THE DUTY IN QUESTION IS CONCERNED THEY PLACE SPECIAL EMPHASIS ON ITS POTENTIAL EFFECTS ON THE FORMATION OF MARKET PRICES AND ON MARKET SUPPLY . THEY ALSO SUPPORT THE ARGUMENTS PUT FORWARD BY THE CATTLE EXPORTER WHO IS THE PLAINTIFF IN CASE 71/80 , THAT SUCH EFFECTS HAVE IN FACT APPEARED ON THE MARKET IN CATTLE . OWING TO WHAT THE PLAINTIFF DESCRIBES AS THE SPECIAL SITUATION OF THE MARKET IN CATTLE IN IRELAND , EXPORTERS HAVE NOT BEEN ABLE TO PASS THE DUTY ON TO PRODUCERS . MOREOVER , A VERY CONSIDERABLE NUMBER OF CATTLE WERE SOLD AND SLAUGHTERED JUST PRIOR TO THE INTRODUCTION OF THE DUTY , WHEREAS MARKET SUPPLIES DECREASED SUBSEQUENTLY , AND THE RESULT WAS AN INCREASE IN IMPORTS FROM NORTHERN IRELAND OF CATTLE WHICH WERE EXEMPT FROM THE DUTY IF SOLD TO A PROCESSING UNDERTAKING WITHIN 14 DAYS OF THEIR IMPORTATION . THE ABOLITION OF THE DUTY PRODUCED THE OPPOSITE EFFECTS . ACCORDING TO THE PLAINTIFFS IN THE TWO MAIN ACTIONS THE DUTY THUS AFFECTED THE MACHINERY FOR THE FORMATION OF MARKET PRICES , MARKET SUPPLY AND INTRA-COMMUNITY TRADE , AT LEAST IN THE CATTLE SECTOR .
17 THE DUTY IN QUESTION CAME INTO FORCE ON 1 MAY 1979 FOR MILK AND BOVINE ANIMALS AND ON 1 AUGUST 1979 FOR THE OTHER PRODUCTS SUBJECT TO IT . IT WAS ABOLISHED FOR ALL PRODUCTS ON 31 DECEMBER OF THAT YEAR . CONSIDERATION MUST THEREFORE BE GIVEN TO THE TRENDS WHICH BECAME APPARENT ON THE MARKETS IN QUESTION DURING THE PERIOD FOR WHICH THE DUTY WAS IN FORCE AND , IF NECESSARY , TO THE QUESTION WHETHER SUCH TRENDS ARE TO BE IMPUTED , AT LEAST IN PART , TO THE EFFECTS OF THE DUTY DISREGARDING , HOWEVER , THE TEMPORARY EFFECTS PRODUCED IMMEDIATELY BEFORE AND AFTER THE INTRODUCTION AND ABOLITION OF THE DUTY IN SO FAR AS THOSE EFFECTS MAY BE CONSIDERED AS THE CONSEQUENCE OF TRANSACTIONS EFFECTED IN ORDER TO EVADE THE DUTY .
18 DESPITE THE LOW RATE OF THE DUTY AND THE LIMITED PERIOD FOR WHICH IT WAS IN FORCE , SUCH AN EXAMINATION IS NECESSARY BECAUSE THE TAX SCHEME AT ISSUE BEFORE THE NATIONAL COURT CONCERNS PRODUCTS WHICH , WITHOUT EXCEPTION , ARE SUBJECT TO A COMMON ORGANIZATION OF THE MARKET AND BECAUSE IT APPLIES , MOREOVER , TO STAGES IN THE MARKETING PROCESS WHICH COINCIDE LARGELY WITH THOSE ENVISAGED BY SUCH ORGANIZATIONS .
19 IT IS FOR THE NATIONAL COURT TO DECIDE WHETHER THE CHARGE WHICH IT IS CALLED UPON TO CONSIDER HAS IN FACT HAD EFFECTS WHICH OBSTRUCT THE WORKING OF THE MACHINERY ESTABLISHED BY THE COMMON ORGANIZATIONS OF THE MARKET . WITH A VIEW TO THE DECISION WHICH HAS TO BE MADE IN THAT RESPECT BY THE NATIONAL COURT IT IS , HOWEVER , POSSIBLE TO IDENTIFY CERTAIN FEATURES OF COMMUNITY