Newshub Political Editor Patrick Gower has warned the Green Party might block a coalition deal between Labour and New Zealand First.
Appearing on the AM Show on Wednesday, Gower said the Green Party membership would need to be consulted on any deal to support a Government - and this would require 75 percent approval.
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"There is a major stumbling block to negotiations and it's the Greens," he said.
New Zealand First leader Winston Peters has said he will only negotiate with Labour, and not the Greens - even though they may end up sitting around the same Cabinet table together.
Gower says that this means any deal cooked up between Labour and NZ First might not be acceptable to the Greens' base.
"The big problem here, and why it's a stumbling block, is if the Greens are offered an inferior deal... you might find that those Greens out there that have fought for that party through some pretty difficult times say 'no'," he said.
Mr Shaw has said "the most likely scenario" is a new Government led by Jacinda Ardern. However when asked about how the Greens could work with New Zealand First, Mr Shaw said that it comes down to all of the parties being responsible and compromising.
Gower says Labour and NZ First need to give Greens leader James Shaw "something decent he can go back to his membership with".
He believes the Green Party wants to do a deal in order to change the Government, but warns they might not accept policies like a dramatic immigration cuts.
"They won't be walked over by Winston Peters," he says. "If the Greens fall over, the left falls over."