The Greens are upset because Finance Minister Bill English won't let the Treasury cost one of their policies.
Co-leader Metiria Turei says the rules allow it but the Treasury needs Mr English's permission.
She wanted it to work out the cost of setting up an independent policy costings unit, something she's promoted in the past.
Ms Turei says that when she first proposed the independent unit in January, Prime Minister John Key dismissed the idea and said it would cost too much.
"By refusing to allow Treasury to cost our policy, Bill English has proven this is why we need an independent policy costings unit which is not subject to political interference," she said.
A spokesman for Mr English told NZ Newswire "we think it's a good discipline on parties that they have the capability to cost their own policies - it demonstrates an ability to govern".