National is still deciding whether it will support the Zero Carbon Bill's second reading, despite reports Judith Collins' plans to vote against the legislation.
But National Leader Simon Bridges has joked that he would find out about what the senior National MP would do in "her memoirs".
This is a reference to the book Collins last week revealed she was writing about her time in politics.
The party supported the bill in the first reading but did not promise to throw its weight behind the legislation when it comes before the House a second time.
National Leader Simon Bridges said although there are major parts of the bill the party does not support, such as the methane reduction targets, the caucus has not yet landed on a decision.
But he said as it is, National is worried about the wider economic effects of the bill.
It is currently in the select committee process where various stakeholders are making submissions.
National will be seeking to make changes in the legislation – "I certainly wouldn't rule out that we may vote against it; that could be something that happens but we haven't made a call yet," Bridges said.
Despite National not yet coming to a decision, Collins says she will be voting against the bill in its second reading.
She did not respond to the Herald's request for comment, but she told Politik she would not be supporting the legislation.
Asked directly if he had talked to Collins about supporting the bill, Bridges deflected.
"I've had many discussions with Judith and with our caucus," but he said he would not "characterise" those discussions.
But he did say he "does not necessarily think" Collins will vote against National on the bill, suggesting National were leaning towards not voting with the Government.
He said: "I suppose we will read about [what Collins plans to do] in her memoirs."
Bridges said he was excited about Collins' book – "she has a busy summer ahead, writing her memoirs and a reformed RMA bill for us [National]."
Even if National don't support the second reading, the bill is highly likely to pass into law as it has the backing of both Government's support parties.