Grain growers want an explanation from merchants after being paid less than half the imported price for their wheat.
New Zealand is not self-sufficient in milling wheat and imports a large amount from Australia each year.
The price gap between prices paid for New Zealand grown grain and imports has been a long-running issue for local growers.
But prices offered for New Zealand grain fell significantly in the final quarter of last year, from about $500 a tonne to less than $350.
Large quantities of New Zealand wheat were sold at the lower prices as growers cleared their silos ready for the next harvest.
The mid-Canterbury grain growers' chairman David Clark says the merchants told them the prices had to drop because large quantities of Australian grain were being imported at much lower prices.
But Mr Clark says import statistics told a different story.
He says the import statistics for the October to December period of 2008 show that there was just over 60,000 tonnes of wheat imported from Australia during that three month period, at an average price of $725 a tonne.
Mr Clark says it shows that New Zealand grain was sold at significant discounts compared to the imported product.
He says there was also 60,000 tonnes of sorghum coming into New Zealand, which is generally a replacement for locally grown barley, and that had a value of $485 a tonne on average.
Mr Clark says they will now contact the Grain and Seed Association to seek an explanation.
He says individual growers also need to ask questions of their grain buyers.