Green co-leader Russel Norman is urging other party leaders to support an amendment to the Mixed Ownership Model Bill to delay any asset sales until a referendum is held.
The bill paves the way for the sales and comes back to Parliament on Thursday. It could be passed into law next week or the week after.
National plans to sell up to 49% of four State energy companies as well as shares in Air New Zealand.
Dr Norman has written to all party leaders outlining his amendment.
He says National has the support only of ACT leader John Banks and United Future leader Peter Dunne for its plan.
Dr Norman says he is confident enough signatures will have been collected by the end of the year to force a referendum.
But the Government intends selling the first lot of shares in Mighty River Power by the end of September.