Packs of McVitie's Digestives will become 20 per cent smaller by the end of this month.
Responding to higher ingredients costs, Pladis, the Turkish owner of the biscuit brand will cut the pack size from 500g to 400g, with the first shrunken products appearing on the shelves at the end of January.
“The rising cost of ingredients and changes in the exchange rates means it has become more expensive to bake our products," Nick Bunker, managing director of Pladis in UK and Ireland.
"We work hard to drive efficiencies throughout our business to absorb cost increases, but occasionally, like many other businesses in these challenging times, we do need to make some adjustments."
He added that the announcement had been made in a bid to be "open and transparent" with customers.
More reductions could be on the agenda, with the company saying it will review a small proportion of pack sizes. One forthcoming change includes the introduction of a larger "value" pack.
The move follows similar size changes by a number of other snack makers last year, in a phenomenon known as shrinkflation.
McVitie's cut the size of boxes of Jaffa Cakes last year, but insisted this was not "shrinkflation" because it also reduced the recommended retail price.
Back in 2016, consumers were outraged over the change in shape to Toblerone chocolate bars, changing the weight of the products in the UK due to cost pressures.