For manufacturer McVities has reduced the number of the tasty treats in each pack from 12 to ten - and the move has met with widespread upset.
The boxes now weigh 4.3oz rather than 5.2oz - but McVitie's has reduced the recommended price from £1.15 to 99p.
Twin packs, which now have 20 cakes rather than 24, are now £1.89 rather than £2.19.
"These changes represent the same price per cake, however, pricing ultimately remains at the sole discretion of retailers," the firm said.
A McVitie's spokesman added: "There is no change in the size, shape or weight of individual cakes in the McVitie's Jaffa Cake range."
But Jaffa Cake lovers have taken to Twitter to express their feelings - and they aren't best pleased.
Lucy Ward wrote: "WHAT!!!! It's not about the price - it's about the 12 Jaffa Cakes in the box!!!!! TWELVE!!!
Rob Moore tweeted: "It takes a lot to outrage me, but just read that @McVities have skunk a packet of Jaffa Cakes from 12 to 10 for same price! #jaffacakegate"
And Jon Shepherd posted: "Today is a sad day. Today is the day that I realise that @McVities are #shrinkifying Jaffa Cakes from 12 to 10 per pack."
Earlier this year McVitie's reduced the size of its dark chocolate digestive biscuits from 332g to 300g - a 10% reduction.