Farmers opposed to Fonterra's share trading scheme have written to MPs considering enabling legislation, to highlight the risks it poses to the co-operative's balance sheet.
Fonterra says it has been keeping $1 billion in reserve to pay for the shares of farmers leaving the co-operative or reducing milk supply.
Trading Among Farmers means those farmers will be able to cash up their shares by selling dividend rights to other farmers or outside investors via a shareholders fund.
Fonterra says that will free up the cash it had been keeping in reserve to pay out farmers for other more profitable uses.
But the Our Co-op group says the legislation for TAF is unclear as to whether it is Fonterra, or farmers who have sold their dividend rights, that would be liable to repay investors if the Shareholders Fund fails and is wound up.
If Fonterra is liable, the group says that could lead to an even bigger risk to the co-operative's balance sheet than now.
The legislation is back before Parliament this week.