The Green Party is concerned by reports of large-scale purchases of Southland farms by a Maori trust with the backing of money from Dubai.
Rural News has reported the trust is negotiating a deal with Dubai World - a subsidiary of the Dubai government - to buy New Zealand farms on its behalf to boost its own food supply.
It reports the trust has signed up 28 Southland dairy, deer, sheep and beef farms.
Greens co-leader Russel Norman says large areas of New Zealand land would effectively be controlled by a foreign government if the deal goes ahead.
Mr Norman says the benefits from selling the food would not kept within the New Zealand economy, but would instead be passed on to overseas interests.
Federated Farmers is urging farmers to be cautious. Its president, Don Nicholson, says it is worrying that a mysterious trust is rumoured to be buying properties when there has been an economic slowdown in the farming sector.
Mr Nicholson says farmers should contact their farm adviser for help if they are approached with a very good sales deal.
The Overseas Investment Office says it has no knowledge of the trust. Its manager, Annelies McClure, says there are strict rules around foreigners buying sensitive land or assets valued at more than $100 million.
Ms McClure says anyone acting for an overseas buyer still has to apply for consent and the Overseas Investment Office does not have enough information about the deal to investigate it.