ADM's decision to increase the price of all its flour by £21.25 per tonne from 15 January comes hard on the heels of its last increase of £28.75 per tonne in September, a 20% rise, which the company blamed on energy prices and poor harvests abroad.
The latest rise - equivalent to an increase of 15% - has led to worries that other millers will soon follow suit with cost implications for retailers and shoppers.
Since August, when ADM announced the September rise, the price of one leading brand of medium sliced wholemeal bread has risen 22% to 94p for an 800g loaf, according to The Grocer 33.
"Bakers cannot absorb the extra costs of flour - and they are reasonably significant increases," said Gordon Polson, director of the Federation of Bakers.
"Retailers may say they don't want another price increase at this time but we've come to the point now when these costs have to be passed on, which is going to result in increased prices. It wouldn't come as a great surprise if other milling companies put up the price of flour."
ADM rival Rank Hovis warned that wheat prices remained "strong", adding: "Further flour price increases are almost inevitable."
A third miller, Carr's, is believed to be considering raising the price of its flour.
Alexander Waugh, director general of NABIM, the millers' trade body, said all milling companies were facing the same cost pressures as ADM.
"If they need to put up prices, they will. It's not great news," he said.
ADM MD Ian Pinner said: "Since August UK bread wheat prices have gone up by a further 15%. We've been absorbing these costs but cannot continue to do this."
John Hastwell, head of marketing at ADM, added: "I guess that over the next month our customers will be talking to the retailers about what they can pass on to them."