New Zealand First leader Winston Peters says Labour must be clear on its tax plans, rejecting the party's policy to implement the findings of a tax review if elected to Government.
Labour may need to form a coalition with NZ First to have the numbers to govern, depending on the election result.
Mr Peters told NZME he wouldn't support any government that wasn't upfront about its plans.
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"You can't possibly mean to go into an election saying, 'My tax policy will be decided by a committee, and I am very sincere about that.'"
Green leader James Shaw, another potential coalition partner for Labour, said Mr Peters was being hypocritical and needed to tell voters how he would pay for his own election promises.
"Winston Peters needs to explain what new taxes he plans to raise to pay for his $10 billion of election promises before he can attack Labour's fully costed fiscal plan," Mr Shaw said.
"Peters has promised at least $10 billion of new spending this election, yet is still to reveal what new taxes he plans to raise or what public services he will cut. Until he's transparent with his own plans, he has no right to attack Labour for theirs."
Mr Shaw said the NZ First leader is holding a potential Labour government to ransom.