The sweet treat has been removed from the £2.99 box - and replaced by the Dairy Milk Oreo.
Fudge, known as Milk Fudge when it first came on the market in 1948, will still be available in the chocolate company's small £1.09 box and its Freddo selection packs.
Cadbury said it had taken the decision "to improve the mix and offer more of a variety for our fans".
But Fudge enthusiasts have not reacted well, expressing their outrage on Twitter.
"Christmas is ruined", declared Twitter user Mark Atwood, while Nigel Quinlan accused Cadbury of waging a "war on Christmas".
Fellow social media user Sinead Gleeson called for "a revolution against this chocolate tyranny".
Fudge joins Dairy Milk, Crunchie, Dairy Milk Buttons, Double Decker and Wispa as one of the company's best-sellers.
More from Food
Demand for folic acid to be added to British flour to help childbearing age women
Man cooks up waffle feast after finding staff asleep
Nestle fined after tests show high ash content in noodles
Is camel milk the next superfood or superfad?
Apple growers face 'catastrophe' without Brexit labour deal
'Alarming' amounts of nerve agent pesticides in world's honey, tests show
A Cadbury spokesman said in a statement: "This year we have updated the range available within our selection boxes to improve the mix and offer more of a variety for our fans.
"Cadbury Fudge is still available in our small selection box and Freddo selection box but has been removed from the medium selection box to ensure we're offering choice between the ranges."