AGRICULTURE - COMMON ORGANIZATION OF THE MARKETS - PRODUCTS PROCESSED FROM FRUIT AND VEGETABLES - PROTECTIVE MEASURES ON THE IMPORTATION OF PRESERVED MUSHROOMS - MEASURES WHICH MAY BE ADOPTED BY THE COMMISSION - LEVYING OF AN ADDITIONAL AMOUNT ( COUNCIL REGULATIONS NO 516/77 , ART . 13 ( 2 ), AND NO 521/77 , ART . 2 ; COMMISSION REGULATION NO 3429/80 , ARTS 1 AND 2 )