Sainsbury's has reduced its packs from 225g to 150g and cut its price from £3 to £2.50 after prices rose following a poor season in Poland, a key growing region for blueberries. Shoppers who previously got 75g of blueberries per £1 now only get 60g.
A spokesman said the retailer had taken the decision to reduce pack size "after much deliberation" and to "continue to offer our customers blueberries at an affordable price".
But Sainsbury's decision has been criticised by some customers, one of whom asked on the retailer's Facebook page: "Is it because your Polish suppliers have suddenly gone greedy... or is Sainsbury's pulling a fast one?"
Meanwhile, Waitrose has pledged to help British growers increase their production levels and extend the British season, after it was unable to source as many homegrown blueberries as it would have liked.
Waitrose said it had managed to stock 90% British blueberries until the end of July, but the fall in UK crop levels meant that from then on British supply had made up just 15% to 50% of all blueberries sold in the retailer.
"Strong winds have resulted in a berry drop on UK farms, and fruit from Norfolk was lost after a late severe frost," a Waitrose customer services rep wrote on the Waitrose online forum. "Our supply is driven by what is actually available. We'd like to be sourcing a higher percentage ideally 100% British."
Waitrose believed the UK was currently five years away from being able to deliver a "solid run of British blueberry supply", the rep added. The chain was working with growers to "access more British blueberries" alongside looking at storage methods to help ensure a longer UK season, she explained.
In January, The Grocer revealed that blueberries had taken over from raspberries as the UK's second-most popular fresh berry, behind strawberries.