Fonterra Co-operative Group has reduced its forecast farmgate milk price for the 2014/15 season from $7.00 to $6.00 per kgMS.
That represents a total drop in payments to farmers of nearly $1.6 billion from their earlier forecast.
A drop in the milk price from $8.40 last season to $6.00 this season will amount to a reduction in the collective income of New Zealand dairy farmers of around $4.3bn, or 1.9% of GDP.
Today's announcement was lower than most in the market were expecting, and will come as a shock to farmers, Westpac chief economist Dominick Stephens said.
"This forecast is one more reason to expect further downward pressure on the New Zealand dollar," he said. "We expect the NZD to drop to 84 cents in the weeks ahead, and we are forecasting an average exchange rate of 83 cents over the remainder of 2014."