Erica Stanford has called for answers from Labour over whether the party knew about a proposal to entrench part of the Three Waters legislation.
Labour and the Greens last week supported the proposal, which would mean water assets couldn't be privatised unless 60 percent of MPs agreed to repeal the clause.
Entrenchment means legislation could only be amended or repealed if a special majority agreed to it in Parliament. Given it had only previously been used on electoral law, a group of academics subsequently wrote to the Government urging it to "think about the dangerous precedent that this legislative action may set".
The move wasn't supported by the National Party, nor did it support a previous effort by the Government to introduce an entrenchment threshold at the normal 75 percent level.
National's opposition resulted in other parties calling on the Nats to state its privatisation position.
"Where does this issue come from? It comes from a concern and a worry that a future National/ACT Government might privatise water," senior Labour MP Michael Wood told AM.
"[The legislation] was voted for because we stand firmly against privatisation of water assets."
But National MP Stanford, appearing on AM alongside Wood, reiterated her party wasn't interested in privatising water assets.
"We've been very, very clear on that - we will not do that."
She said questions still needed to be answered about the entrenchment issue.
"Did Labour know or did they not know? Was it their Whip that accidentally voted for it? … Who knew? Who voted on it? We voted against it and we've been very clear that this is not the right mechanism to use."
Prime Minister Jacinda Ardern and House Leader Chris Hipkins have said they were aware of the previous attempt to get support for the 75 percent entrenchment but not of the 60 percent provision put forward by the Greens until after the fact. However, Stuff reported on Friday Ardern was at a Labour caucus meeting where a discussion about the entrenchment clause took place.
"The Prime Minister has some explaining to do," ACT Party leader David Seymour said in response to the report. "How was it that this was discussed in caucus, but she claims she wasn't across it?"
Responding to questions from journalists on Thursday about such a meeting, Ardern confirmed she was in caucus when entrenchment was discussed.
"I've also discussed, and pointed out, that entrenchment is generally understood to be a threshold of 75 percent.
"Conversations in [the] caucus are kept in caucus but what we've already said is, we took a view on the principle of ensuring that a public asset, like water, is absolutely protected from privatisation and I think that's a view generally shared by New Zealanders."
The controversial provision has now been referred back to Parliament's business committee.
