While the co-op has been busy outlining to members nationwide, the progress in its business turnaround, it says the market has weakened further.
Consequently, said a spokesman, as a result of falls in the market mechanism that governs its returns, price changes need to be implemented.
The May price changes:
The cuts follow similar announcements by Muller and Dairy Crest last week.
Read more here: Muller and Dairy Crest announce June price cuts
Last week First Milk chief executive Mike Gallacher told members the business was expecting to deliver an operating profit (before restructuring costs) of £4 million for the year to March 31, versus a loss of £20m for the previous year.
The debt of the business had reduced to £33m from a peak of £84m in 2014/15.