1 NEWS' Political Editor says the theme of the past few days has not been to Labour's advantage and they had to do something.
Speaking on 1 NEWS' Midday news today, Corin Dann described Labour's black flip on tax as "huge".
"In the context of this campaign, to come so late in the piece after so much pressure has been on them, they've clearly been rattled," Dann said.
"And what they've done here is decided that, frankly, the damage inflicted upon them, on this issue of tax, has simply become too much and that out-weighs any damage that might now come to Jacinda Ardern over this issue.
"Because, remember, she made a captain's call to go with this policy of a working group on tax and leave open the possibility she might use it to implement a capital gains tax if that's what it recommended, during her policy.
"So the change in the policy today means they would have to go to an election before they do that.
"That was the old position that Andrew Little had.
"So an extraordinary turnaround."
A new 1 NEWS Colmar Brunton poll, out tonight, will reveal the true extent of the impact National's attack of Labour's previously murky tax policies has had on Labour's vote.
In the last poll, seven days ago, Labour had extended their lead from 2 points to 4 points, on 43 per cent, with National on 39 per cent.