Council chairman Simon Couper had sent a message to shareholders and board stating that when it came to trading among farmers it was 100 per cent shareholder ownership and control of the co-op or nothing.
"Farmer ownership and control of our co-operative is essential to our core beliefs," Couper said.
"If there is any real risk that 100 per cent ownership and control is not retained by our co-op, council will not vote to support moving to [trading among farmers]."
The council had retained a lawyer with extensive senior corporate law and Government advisory experience who was constantly reviewing and questioning the provisions contained within the structure, he said.
"From the council's point of view it is 100 per cent farmer ownership and control of the co-operative or nothing - if our review process shows that this most key aspect of [trading among farmers] is not guaranteed then [trading among farmers] will not go ahead."
Fonterra chairman Sir Henry van der Heyden last month sought to reassure farmers about control of the co-operative.
"You voted for 100 per cent control and ownership 15 months ago," van der Heyden said in an email. "That's what we will deliver."
The due diligence committee, management and board would all sign off on the co-operative staying controlled and owned by farmers before the proposal was taken to the Shareholders Council, he said.
The proposal needs legislation which Agriculture Minister David Carter has said is unlikely to be passed before the November election.
Spierings, who in 2008 led Dutch dairy co-operative Royal Friesland Foods into a merger with Campina, creating Royal FrieslandCampina, is due to take over from Andrew Ferrier as chief executive of Fonterra on September 26.