"A successful bid by an overseas company for a significant chunk of New Zealand's productive farmland will have implications for our future as a nation which relies on dairy for export earnings.
"Announcing any decision a day or two before Christmas will likely stifle public debate on an issue which has vital significance for New Zealand's economic sovereignty."
An OIO spokesman said Milk New Zealand's application was still under assessment.
"There is some key information that is still outstanding, so the OIO is not yet in a position to submit its report to minister," he said.
"The OIO does not know at this time when a decision will be made."
On that basis, the spokesman said it was unlikely the OIO's decision, which then has to receive ministerial approval, would be reached before the Christmas break.
The OIO considered it was still within its 70-working-day timeframe to reach a decision because it excluded time spent waiting for additional information from applicants.